First off, I agree that SLI is completely pointless if you want an Ati card. It also doesn't help all that much, and by the time you <i>need</i> a vid card upgrade, you'll likely find there's a better alternative single card anyway...
Save the cash and don't get an SLI board, basically.
If you're not overclocking, just buy a boxed CPU then you get the AMD retail heatsink, and won't need to bother with that thermaltake thing. I'm using the stock HS on my 3200+ A64, and I'm overclocking, so it'll be fine for a non-oced system. (although I'm shortly going to get a ThermalRight XP-120 anyway, so I can overclock and suffer less noise at the same time).
Also, if you can, try to get a 'Winchester',(90nm) core A64 instead of the Newcastle (130nm) (IIRC the 3500+ is available in both cores). It runs a little cooler than the newcastle. Not that much in it, but every little helps
Aside from all that, I can see you've already put a decent amount of research into this. Well done! Quite rare to see that, normally people don't bother, but that's a bit lazy really....
Don't forget you need to get an OS too. Windows XP is not cheap (unless you happen to have the right friends of course... *cough*oneswithafastinternetconnection*cough*)
For office stuff (word, excel, etc) there's openoffice.org. I've been using it for a month or two, it can read and write files in Excel/PowerPoint/Word format, and is a completely free and legal ~50Mb download. Hell, I use it at work even though we have MS Office here, because I don't think it has pinball/flight simulators/etc pointlessly built in & consuming resources.
---
"Sex without love is an empty experience...
But as empty experiences go, it's one of the best" - Woody Allen