I started a similar project at the end of last year. Check my sig to see what I bought! This whole lot will probably cost you between 1000 and 1500 euro. Its the 'limit' so to speak; the only thing missing is a pci busboard and a voodoo card. But I prefer Bvision coz its an 'Amiga Thing'. Also I love the shape of the card

However.. I do not recommend this approach to you. I had a LOT of trouble getting everything working together (although the people on this site helped me out a lot). If you are completely new and dont have much time and/or money, stick with the best accelerator made for the a1200: the blizzard 1230IV/50. Get a 32MB simm and a harddrive/sdcard. Perhaps an internal flickerfixer (ofcourse, the indivision1200) too. You can stick with the standard desktop case for now, it really gives you something to show off

You can even get a cdrom drive and let the cables hang out of the a1200 casing until you need it.
Then spend a year or so figuring stuff out (whdload is the best waste of time you'll encounter) and later on decide whether you want to go further with ppc/pci/os4.