Congratulations!
You've been getting good advice on your 7s. As others have said, it's a top-grade, highly sought-after camera. If you can't use it for your class, and if you don't want to keep it for your own use, and if your dad doesn't want it back... well, don't let your local camera store talk you into accepting $50 as a trade-in value for it!
I'm going to discuss the CLA, lens and meter issues at some length:
CLA -- No disrespect intended for those who recommend them, but I'm not that big a believer in routine "CLA" (clean, lubricate, adjust) services, unless the camera really needs them (see below.) This is especially true with classic Canons -- their shutters are an excellent design, but it takes a real Canon expert to do a good job of adjusting one. Once adjusted by an expert, it will be quiet and very accurate for years and years. A regular joe-blow camera repairman might be able to get it going, but it won't perform as well.
So, does your camera need a CLA? I would say first to try all the shutter speeds. The shutter should "buzz" smoothly (no hesitation) at the slowest speeds, and "click" solidly at the higher speeds. Take off the lens, open the camera back, and point the empty lens opening toward an evenly-lit (not fluorescent-lit) white surface, then watch through the shutter as you fire it at each speed. The shutter curtains should snap open and shut briskly, and you should see even lighting across the shutter opening (not darker at one edge or the other.) Try it a few times -- you'll be surprised how well you can "eyeball" this, even at the fast shutter speeds.
If the shutter seems to be working smoothly, the viewfinder surfaces are reasonably clean, and all the camera's controls seem to work, then I would say your camera may NOT need a CLA. At least put a roll of film through it (or get a camera-savvy buddy to do so, if you aren't sure how to use a manual 35mm camera yet) and base your judgment on that.
Meter -- Before you conclude that the meter is bad, there's one weird little thing you might want to try. The 7s meter has two sensitivity ranges; you set them by rotating the knurled collar around the sensor eye on the front. You'll notice this collar has two settings, "H" (high sensitivity, for use in dim light) and "L" (low sensitivity, for use in bright light.)
If the lighting in the camera store was fairly subdued, and if the person helping you had the meter set to "L", the needle would barely budge even if the meter was working properly! A lot of camera-store people don't know about this. So, put in a Wein Cell and try again, making sure you set the sensitivity control appropriately.
If the meter still doesn't work, then it does need repair. The fact that the battery check makes the needle swing proves that the meter movement itself, and all the wiring from the battery compartment through the switch, are OK. About the only remaining piece is the sensor cell. This is a CdS-type cell, and it's unusual for them to just "die", so it's more likely that one of the wiring connections or solder joints has gone bad. A good repair-person could likely fix it, but the top cover will have to come off, so it'll be a relatively expensive repair to do by itself.
If you do decide to have a CLA done, the top cover will have to come off anyway, so you should get an estimate on getting the meter repaired at the same time. The camera is worth more with a working meter, so you'll probably want to have it fixed if the extra cost isn't too high.
Lens -- The easiest way to deal with your foggy lens is to swap it for one that isn't foggy. Someone else recommended the Canon 50mm f/1.8, which is an excellent lens, and the later black-and-chrome version is the correct type for your camera (which will improve its resale value if you decide to sell it, vs. fitting a non-Canon lens.) But you probably won't be able to get an even swap of your foggy lens for a non-foggy one, so you'll be out some money.
A professional cleaning also will probably fix your lens, but that also will put you out some money.
What I'm about to tell you is drastic, and I recommend that you do NOT do it if you're even slightly uncomfortable about it! Ready? Well, open up the aperture of your lens all the way, and examine the glass carefully by shining a small flashlight through it from one end as you look from the other. Look carefully at WHERE the fog seems to be. Does it seem to be on all the surfaces of the glass? If so, stop reading and go back to the suggestions above.
But, if it seems to be ONLY on the surfaces in the middle of the lens, you may be able to do something about it, if you're both dextrous and very, very careful. The most common place for these Canon lenses to fog up is in the center, on either side of the aperture blades (the fog is caused by oil vapor from the focusing mount) and this surface is accessible for cleaning by splitting the two halves of the lens.
Remember, don't try this if you're even slightly unsure about it -- when it's in good shape, this lens is worth a lot of money, so you don't want to ruin it and destroy its value by a botched amateur cleaning! Still game? Well, you need a very, very tiny jeweler's screwdriver -- a #1, or 1/32". This is probably the smallest in those six-screwdriver sets they sell in camera stores. DO NOT try to use any substitute, such as the tip of a knife or any other goofy thing that might occur to you -- it's either a #1 jeweler's screwdriver or nothing! OK, still game?
Now, sit down at a clean, well-lit surface, spread out a soft towel on it, and take your lens in hand. Make sure it's set to maximum aperture, f/1.2 Look at the front part of the lens from the side, around the front trim ring that's just ahead of the movable aperture ring. At what would be about the 7 o'clock position (with respect to the front, with 12 o'clock being the top) you'll see a tiny, tiny black setscrew.
MARK the position of this setscrew relative to the black edge of the lens ring in front of it, using a felt marker or a little piece of tape. You'll need to be able to find this exact position later. Now, CAREFULLY fit your #1 screwdriver into this tiny screw, and loosen it. If it won't turn, STOP! You don't want to gouge up the screwhead, so if it's stuck, give up and leave the job to a professional. If it will loosen, back it out so it sticks up just a bit. (Don't take it all the way out; it's not necessary, and this way you don't risk losing it. It is REALLY small!)
The screw you have just loosened retains the front lens assembly. Once the screw is loose, you can grab the very front ring of the lens by circling your thumb and forefinger around it (this distributes the force) and unscrew it counterclockwise, just like a jar lid. If it seems to drag, loosen the tiny screw a bit more to make sure it's not scraping as you turn the ring. BE CAREFUL not to cross up the threads, drop the lens, or do anything else goofy! Unscrew the front assembly until it comes all the way out. Set it down carefully on the soft cloth.
Now you can see the two interior surfaces of the lens: one on the back of the group you just removed, and the other down in the "cup" it unscrewed from. If you're lucky, the fogging will be confined to these two surfaces. You really, really, REALLY don't want to scratch them, so here's how to clean them: Get the oldest, softest, most-often-laundered cotton handkerchief you own. Make sure it's absolutely clean and really, really soft. Now, breathe on one of the inner lens surfaces to steam it with your breath, and then gently wipe off the steam with the handkerchief.
If you're lucky, the fog will come off with it. If not, leave it alone -- you don't want to risk scratching the glass! After you've cleaned one surface, breathe on and clean the other, using a different part of the handkerchief. When you're wiping the surface that's down in the "cup," don't press hard around the edges -- you don't want to disturb the aperture blades, which are very delicate.
If the lens is now clean and clear, great! If not, there's nothing more you can do -- don't be tempted to try to take it apart further! Either way, it's now time to reassemble it.
Set the front group you unscrewed earlier gently into the "cup" from which you unscrewed it. Try to get it sitting as squarely as possible so you don't damage the screw threads, which are very fine. Turn it gently until the threads catch, and screw it down. If it resists, don't force it -- back it out and try again.
Tighten it down until the mark you made JUST lines up with the little screw -- no more, no less. Now tighten the little screw until it just bottoms -- be gentle, don't force it.
If everything went right, you now have a good, clear lens that's worth a lot more than it was 10 minutes ago. But again, the penalty for screwing up is severe -- you could ruin a lens that's worth a lot of money -- so don't try this unless you're sure you're up to it, and don't blame me if you screw up!!!
