Although I started doing photography in 1954 and am well accustomed to hand-held metering, I would advise looking for an M6. The M5 was too bulky and mechanically complex. While screw mount Leicas are great, they only work well with the 50 mm lens and if you want interchangeable lens capability, they are clumsy to use.
Leica got it right with the M 3/2/P etc. size and shape. All their other attempts were off in one way or another, IMHO. Even though the M6 does not have the ultimate mechanical finesse of the earlier Ms, it is the best of them for street photography because of the built-in meter. Yes, separate and no meter has worked for lots and lots of photogs, but it is a handicap to not have one inboard all the same.
My first Ms were a 4 and a 2. I, too, used them with an accessory meter. The M4 came with an outfit that included an MR4 clip-on meter, which speeded things up a bit but added bulk. I preferred my hand-held Sekonic to it. In 1968 I added a Pentax Spotmatic to the kit for long lens use and immediately learned the value of being able to set the exposure as I composed the photograph. For a long time I used SLRs in place of Leicas for most of my photography on that account. Even today, I consider the built in meter the most significant technical development in the evolution in camera design and all the rest merely incremental improvements. This, of course, is based on my preferred subject matter and way of working.
At first I considered the 50 mm lens as just about perfect. After years, I thought the 35 mm was the bee's knees. I think the M6 works best with these two, although it's entirely your call. Nothing is more subjective than how you view things.
The M6 with its meter represents the best 35 mm "candid camera" available because it is fast (er) and focusses more accurately than an SLR. I believe its reputation among "slice of lifers" is well earned.
