Ok, first of all don't make any rash decisions; you'll regret them later.
I suggested an 030 with 8Mb of RAM because it will give you a fairly powerfull 1200 with which you can do a lot of stuff without too much trouble. Like gaming from HD and comfortable use of Workbench and other apps. It can run 3.9 too but you don't need that. So you don't need a buffered IDE interface, network card for 3.9 to work but you do need the OS3.9 CD and a way to get it on your HD. My advice is to just stick with 3.1 for now. Even with a 4Mb RAM card your 1200 will feel faster and can do more things.
What would you do with a PPC card if you don't even know what you want to with a stock 1200? Don't trade your Xbox for something you don't have a clue about what you're gonna do with.
Please first make up your mind about what you want to do with your Amigas.