Building a system usually cost more than buying a whole system .The A3000 is somewhat hard to find and parts are tough too! The A3000 is also a little more costly than some of the others.I have owned a A3000 and you have chosen a great amiga ;so have fun either way.
As far as what to get well that depends but this is what I would do.
Video card-I would suggest the picasso IV,Retina.
Accelerator- 3640 is really pretty good but if you want speed 68060 is the way to go!PPC is really awesome you would be able to get OS4.Cyberstorm MK 3 is a good one.You would also get a faster scsi controller with it also.
Upgrade OS- at least to 3.1 but 3.5 and 3.9 are also good.
Max out memory. should have 2mb chip and 16mb fast ram.
Upgrade Scsi controller chip to the new Western Digital I belive its version 08( I could be wrong) If you use a accelerator card with scst no need for this!
That's the big stuff I did not include any video production stuff are sound which I would also have.This is already long enough now.As far as keyboards and mouse get whatever one you like.I would say stick with amiga KB and mouse because they work and pc crap does not ( at least not as well).
That cd rom in the performa has to be IDE and will not work unless you have a IDE controller card.You could get a catweasel/budha that would get you ide and you could read all kinds of floppies.Ebay has some things and software hut (softhut.com)is a good place also.
Hope this helped some.
Thank You
:-D
