David, yes, more spindles is good. Lots more is better! I should have clarified. I recommend figuring how how many spindles you need (or can afford), but then getting the largest drives you can manage. A bad thing to soon be running at 80% drive capacity, for space that is. I agree with Steve, more controllers are better, though I'd say it depends on what kind of controller. Onboard memory really helps, I think ours has 512m maybe??
I use R5 for data, R1 for logs. Raid 10 would be nice, but cost is high and for the load I currently have, R5 is working fine. Even with the 240 or so log files I have on the R1, average utilitization is maybe 10%. I know the numbers support R10 for anything over 10% writes, but I think that number is low, don't be afraid to deploy R5!
I definitely support building in redundancy, UPS, fans, whatever. We bought an 8 way Dell box last year with a 10 disk external Fibre setup, total with a enclosure, UPS, everything except software was $80k. That's a lot if Im writing the check, but for a corporate purchase, given how important it is, not bad at all.