Well,Walther forums in general, and certainly this P5 forum, are about as dead as a forum can get. As to the P5 variations, I have a few of the different ones. I can't really discern any significant difference in quality or function. The later mag release is probably less likely to be accidentally pressed. After about 1990 and about serial number 100,000, Walther changed the gun somewhat to make it more resistant to accidental discharge if dropped. They offered a retrofit to older guns also, and as far as I know there is no marking to indicate if a gun was sent back for the modification. I have never bothered to try and look at this difference, and wouldn't worry about it myself. There are reports of P5s being sensitive to some ammo, especially gold dot and 147 grain ammo, perhaps due to excessive OAL. I haven't had this problem though, so have no idea whether it is limited to certain years. I am sure the gun was primarily designed to work with NATO spec 124 grain, though, and so my first choice in carry ammo would be 124 grain non +p Federal Tactical or Winchester Ranger T, although I also use the 147 gr. Ranger T with no problem. I think it might be a little hard on the gun though, long term, so I prefer the 124.
For all the talk of the P7 cult (no offense to anyone), if there is a cult surrounding any 9mm gun of recent manufacture, I think it would have to be either the H&K P9 (which doesn't fit my hand at all), the P88, which is a bit big with a bit of a wide grip and very expensive, and the P5, which I like better than my P7 or Sig 225.
Excellent gun, under appreciated. Consider replacing mag springs and if you are up to it, recoil springs too. If the factory grips seem to slim, get some Hogues or spring for the Nills if you want wood.
There are a bunch of German police trade-ins around now, with some at reasonable prices, although I have not looked at any and don't know what kind of shape they are in.
I hope you find a good one at a good price. Welcome to the cult.