I agree with John that any books you buy will be an important part of your investment! Of course this site is a great start, just read through old posts in each section and you will be pleasantly surprised how much info is here!
Be careful, it is easy to spend too much, but on the other hand, a good shooter can be had for $450 - $600, depending on where you live and who's selling. BUT, many times a nice "collector" piece can be had for the price range you are looking at, any collector piece will always be worth more ten years from now than a mismatched piece. If you damage a "numbered" piece on a Luger, the value does drop, so that needs to be taken into consideration, but, I have shot many rounds through my 1914 Artillery and have never broken a part either, so...