Any put together gun, well, I don't know till I shoot the heck out of it, so #2 above is harder for me, if I have shot it and it is reliable as all get out, then I probably wouldn't sell it.
If you are looking for a totally reliable gun, then maybe something besides a luger, a glock perhaps or like the p38 I was selling, it just shoots and shoots with no stoppages?
Retail Values, visit the gun auctions and places like Simpson's LTD (see ref section here on the left).
Rough values, expect to pay $500 to $600 just for a beater luger, $700 - $800 for a nice low end collectable shooter.
for #3 above, expect to pay $900-$1200 (except what is a exc condition refinish, a East German gun, because a Weimar or nazi refinish, you'll pay what an original cost.
for #4 above, anywhere from $500-$700
A 30 luger (aka 7.65mm) will be the cheapest in the nicest shape. You can usually get a nice one for $500-$600, a almost mint one for under a $1000... The 7.655mm just do not sell very well to the average guy, they want a 9mm to shoot often and cheap...
Ed