1st don't think twice about ASUS it's the no.1 Motherboard Manufacturer for years and they have a great researches and development team always bring to us great technology. This is a server and workstation motherboard so don't worry about CPU overload specially most ASUS M/B run a special overclocking technology to provide best performance.
2. You know most of the Motherboards manufacturers recommend windows as operating system but you can find Linux drivers to get the advantages of all motherboard features just go to their download section if you didn't find anything just contact their support team and don't worry they'll do their best.
3. Do some googling you'll find big list, I found these for you.
$46.99 - G.SKILL Ripjaws X 4GB (2 x 2GB) DDR3-1600 8-8-8-24 1.5V
$59.99 - G.SKILL Ripjaws X 4GB (2 x 2GB) DDR3-1600 7-8-7-24 1.5V
$99.99 - G.SKILL Ripjaws X 8GB (2 x 4GB) DDR3-1600 8-8-8-28 1.5V
4. Any manufacturer gets a list of memory vendors and test them on their motherboards they can't do that on all vendors because you have more than thousand of memory vendors around the world. Yes you can use any brand but most trust-able and safe are the one listed to get better performance.
Maybe OT, but you posted in "dedicated server"... no IPMI/KVM integrated in that motherboard? I know some of the ASUS boards do have it.
Agreed with Dougy, go with software RAID over "on-board" aka "fake" RAID. You are correct that the onboard RAID probably wont work even if you wanted it with Linux. I have a dell PC that acts that way, the drivers are only for windows.
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Considering the supermicro alternative at that price INCLUDES IPMI/KVM it might be worth a little more thought. Just saying, because I know that 10 minutes waiting for a DC to hook up your external KVM can be the 10 minutes that causes the customer to complain.
Well further looking into it, it seems that the asus motherboard comes with KVM called ASWM2.0 which allows for KVM. Not sure if thats integrated into the MB but im sure as long as there is internet connectivity and the server is online this "KVM ASWM2.0" should work?
Thanks for the information we didn't list the information to target anything as we told you before this is just an example don't need to use it and stick with it. Just google for what you need and you can find many threads about that from there we got these information.