I've had a few A3000's and they are awesome but if I'm gonna spend some money, might as well get the machine I've always wanted..
For sure... the A4000 has always been my favorite, as well. :-)
I don't know of a good place to get the gear anymore...
But if your accepting recommendations on WHAT to buy, I'd humbly suggest you should pass on the 3640 card. They are way too expensive for the poor performance they deliver. (The RAM accesses to the A4000 motherboard are WAY too slow! -- My A1200/030 @ 40mhz "felt" faster than my A4000 back when it ran the stock 3640.)
Go for a CyberStorm or WarpEngine card that has the RAM on-board the card. The performance difference is WELL worth it. If you can't get the fast CPU card right away, just pick up one of the really cheap 68030 boards to use until then. The CPU 030 itself isn't as fast as the 040, but the 3640 board is so hampered by the slow RAM accesses, I didn't notice a real speed difference between the two cards (except while rendering). Take it from a user who's run all three. If you really want it to be "the machine you've always wanted" go for the CyberStorm or WarpEngine. :-)
(Personally, I just regret that I only have a CS-MKII, and not a CS-PPC.) If I could ever find a known good one at a reasonable price..........