I would say check the price on Windows XP Pro, to see how close it is to the home version. The pro version is a bit more robust, in my opinion.
I would suspect that by the time you seriously consider SLI, there would be better mtbs out there, so I'd say the planning for SLI for this board probably wouldn't get you much.
Now I'm not an audiophile, hell waaay too many guns and rock bands put an end to that...
I'd suggest you hold off on buying a sound card and see how the on-board audio works first. On-board sound seems to work for me just fine and it will save you bucks, that you could use elsewhere. If you try it and decide it isn't doing a good job, then get the sound card.
So far the only complaint, I've heard from my squad-mates is that I talk to loud on the mike, (of course you'll have to ask them to be certain...
). And that's just a mike adjustment. On-board audio has been fine for me.
Now I've been an Asus fan for years myself and have had very good results for both myself and my clients using the 'under $200.00 boards. I'm currently running an Asus dual Xeon mtb and it's been great and even runs Vista, (not that I'd want to just yet). I'm not familiar with the mtb you selected though, so I don't know how it compares. I would take a hard look at the Asus P5 series of boards. The P5E series has received some nice reviews, although I'd probably go with the 35 chipset instead of the 38chipset.
Check for some reviews of the 35 chipset mtbs and see how your mtb compares against the Asus boards before you finalize your choice. Your board uses a different chipset so you'll have to do a rough compare, but it should help.
I am not a fan of Raid at all. It protects you against hardware failures, but not software failures, ie; windows corruption, etc, etc. And you're more likely to have a windows corruption then a hard drive failure. Less then 4 weeks ago I had to recover files from a customer's system that was running RAID. Windows got corrupted and the RAID system mirrored the corruption to the second RAID drive, so there was no recovery possible. I was forced to use file recovery software to recover his data.
I then set him up with a non-raid system, and used Acronis True Image to create a full image backup of the system and data. This protects against both hard drive and windows corruption and IMHO, is better than using RAID.
I'm also not much of an overclocking fan. I've never felt the need to stress any of my systems out to the limit just to squeese a little more out of the cpu. Never felt it was worth the cost for what ya got back, but that's something you'll have to decide for yourself.
Other then that I think you'll be wery wery happy with your choices.
Wabbit