Hi,
I might as well throw in my 2d worth. I can remember the sensation the OM-1 caused when it first appeared in the early 70's and then the second sensation when lens tests started appearing that made it a benchmark for the others. It also inspired a range of small cameras from all the other makers as, until then, they were all large and heavy. It's best point, apart from the lenses, were the screen - big and bright - and the lack of all that noise from the shutter.
I had the OM-1N years ago but got rid of it when I got the OM-2N which offered the best of both worlds, meaning manual with TTL match needle metering and aperture priority. I also had an OM10 as a spare body, which was purely automatic but had a brilliant manual adapter available.
I still have the OM2N but started looking around a few years ago for one of the first OM-1's, meaning the version before the MD OM-1. I eventually found one in good condition but with foam rot affecting the prism. I had a word with Michael Spencer who was able to fit a newer and better prism from an OM10. He also converted it to take the SR44 battery instead of the old mercury one. I also searched for a type 1-13 screen for it as I preferred that style of screen. They are easy to find on ebay and very, very simple to change.
I also sought out another OM10 as they are available dirt cheap these days, which is a pity as they are good cameras with a brilliant metering system. If you just want to "taste" the system then look for an OM10 as they often come very cheap to cheap with the standard f/1.8 lens and have a hot shoe that takes the (also cheap) Olympus T20 flash. They also make excellent second or back-up bodies if you get serious about the range. Like the OM-2's they need two SR44 batteries. (The OM-1 took one mercury battery.) Take two SR44s with you if searching for them, they will enable you to check the camera without locking up the mirror.
The range of lenses is second to none in my opinion and there are several accessories for the camera that make it even easer to us, for example, the bracket for the flash that raises it high above the camera. BTW, the hot shoe is detachable and comes in several versions. Some have right hand threads and others left hand threads, so no problems getting the wrong one.
A minor point, the OM-2's mirror will lock up if it is wound on when the battery is dead or missing. Turn the battery switch to "check - reset" and it will come down. The other point is to look for a body and then the f/1.4 standard lens which many see as a bargain these day. The f/2 85mm lens is the one that everyone chases after. If you get the chance go for the original Olympus metal lens hoods, the Olympus rubbery ones are not so good but are cheap and plentiful. A lot of the lenses take 49mm filters, which is useful.
Regards, David