Don't worry, I understand the english - though at first I though you wanted to know what would be good to throw at it :-o :-)
Are you sure that the slimline CD will fit in the floppy drive space? IIRC the photo you might be thinking about had the A1200 housed inside an A500 case. And if you do decide to do that, you'll need more IDE equipment to hook it up.
You can easily upgrade the processor/RAM with the "trapdoor" under the case. You can upgrade it to a 68060 @ 60/70 Mhz or so and shove some more RAM into the accelerator card.
There are other upgrades as well such as soundcards, but do remember that the A1200 was never intended to be heavily upgraded - if you want the latest and the greatest you'd need to put it in a tower. Also, watch out for the power if you are adding loads; the original A1200 PSU is puny - it's worse than the A500 PSU.
