First of all you need a tower... and for the stuff you have mentioned, LOADS of cash

Now for the mediator - yes when I tried a Mediator project I had loads of problem with the Blizzard 030, and also had same problems with Apollo. I had an old version of the mediator though, maybe they fixed the problems.
Anyway, it all boils down to what you plan to do...
An "ideal" amiga 1200 would be:
Tower
Mediator
Voodoo Graphics Card
Network Card
Soundcard
Kickstart 3.1
VGA Monitor for OS3.9
RGB/Scart monitor for games
PPC with 060 and loads of RAM
FAST ATA 3
PCMCIA 90 degree adapter
DVD-ROM
HDD
If like me, you only want to play games, the following would be enough:
Desktop A1200 with Blizzard 030 and extra RAM
External SCSI CD ROM Drive
Squirrel
Internal 2.5HDD