I built my server using an Asus mainboard too. Good quality board with quality caps, etc. Only problem i ran into was installing the drivers from the Asus install disk. It did not list Windows Home Server as one of the supported operating systems, so it would not install. Browsed down the disk to the individual driver install apps, and ran them each directly and they installed just fine. It was 6 or 8 drivers iirc.
That was about a year ago and the server is running fine. Just upgraded to WHS 2011, and i like it a lot better than WHS v1. It streams fast (1080p through cat-5 to WD TV LIVE Plus HD) , has file duplication on different physical hdd's, backs up all the household PC's, holds all the family photos and video as well as ripped music CD's and movie DVD's for playback throught the WD TV live plus HD, and most of the time it just snoozes so its not wasting watts. Multiple devices accessing different or same files at the same time are no problem for it. The 3.0 CPU is more than enouh HP. Although the server has 6 TB of disk space, only about 3TB are available because of file duplication.
My Server :
Case - Broadway, Black 943, m-ATX. (didn't know metal could be rolled that thin!)
Mainboard - ASUS M4N68T-M V2. CPU - AMD Athlon II 3.0GHz Dual-Core.
HDD's - (2) WD 2TB Green, (2) 1TB Hitahi Deskstar, (1) WD 160 GB for Server OS backup.
Memory - 8GB DDR3 (2x4G).
O/S - WHS 2011.
Data Duplication: DrivePool by StabilBit.
WHS 2011 can be had new (OEM package) for about $50, and Drivepool is $20. So licensed software is cheap. When I built it, everything except the hdd's ran under $200. It is plugged into a Tripp Lite UPS so power surges and fluctuations don't bother it. The UPS is small, and will run the server for about 3 minutes before sending a signal to do a shut down. That I like.
So what OS are you going to run? Are you going to leave it on 24-7, or just as needed? Going wired or wireless ?
Sounds like you got some good deals and that hardware will build a nice platform for whatever you want to run on it. Good luck with your build!