Let´s start with the beginning. whether your motherboard still works or not. Try to lay your hands on an A500 powersupply, try to get the real heavy ones as they allow you to expand your A1200 much more than the standard A1200 powersupply !!! If you don´t find any then try to convert a PC powersupply to use it on your A1200 using your own chewed-on powersupply plug. You can find documented details on Aminet about this.
As far as expansions for the A1200, let´s say that this is the least of your problems :lol: Just visit
Elbox to get an idea what may be possible for a start :lol: