I need info specific to the A600, on upgrades and stuff.
Ah, stuff. Yes , very important facet that :-D
You can get an accelerator card to get it up to an 030 at 25 or 40 MHz. They're a bit rare these days, but still findable. I got mine from PowerC in the UK. An accelerator card will also let you add more FastRAM (EDO SIMM), but since it's a hack that sits over the CPU, you will probably have trouble fitting the HD in the case afterwards, or if it does fit the chip + HD will overheat and crash very quickly. I should think a Blue Peter-type case mod, involving a cardboard box cut to size, plaster of paris and some sticky-backed plastic (or whatever) to make a little external housing for the HD would be a good idea.
You can also get extra Chip RAM, to bring the machine up to 2 meg. This sits in the expansion bay. Mine came ready equipped, so I don't know if you can still buy them.
OS: even if you have the 3.1 ROM already installed (a Good Idea, since I doubt you'll find fully working copies of WB3.0 very easily these days), don't bother with OS3.9, as the graphic capabilities of an A600 frankly can't cut it here. Even OS3.5 is overkill. WB3.1 is best, preferably teamed up with Scalos or DOpus.
After that, you can always go for the fancy stuff, such as a scandoubler so's you can use a cheap VGA monitor. Beware the Squirrel SCSI interface: it's handy to have, but I find it makes the system more unstable.
Pity we're not in the same country: I could have supplied you with a PSU and mouse. I am
not parting with my A600, though. :-D