Go for the A3000, a 040/40 is miles ahead any 030 and in addition to that the A3000 includes a flicker fixer so you can plug it to any VGA monitor, and you also can expand it easily...
A Cybervision64(not the 3D version) would be a great card for the A3000, because you can plug the VGA output of the A3000 to the passtrough and watch everything in the same monitor.
The A600 is not an option if you are looking for expansion...
You'll be able to watch old QT and AVI videos. MPEG runs slowly (your best bet will be RiVA, the fastest 68k MPEG viewer). With a 040/40 you can play Mp3 quite well, at 44khz mono or maybe you can adjust it to play in stereo at more than 22khz... I guess that you'll be able to get around 33khz at stereo.
