So I have to read MPC's suggestion to try to answer this? MPC is usually 2 months behind, have their flaws, and the forum usually as to debate something that is 4 months old.
Forget everything in that issue. WHS2 is what you want, it still has issues with backups over a set amount of capacity, and you have to deal with it. There's a 2TB limit on backups, so start with that on the server. Make sure all host backups fit on a 2TB drive along with what the WHS runs on. Here we're all SSD's so a 750G drive is an easy %root% drive. After that, you're free to run the HOME server.
No drives have to match, and I think that's good. If you want DVD ISO's to be Drive F:, the do it. If you want MP3's and Video's to be E:, do that too. But if you want all drives to mash up and then sort them out in the OS...that's not what you really want in a server. It's possible though with an ad-on.
Server. Order. You want this. I feel I have an awesome WHS2 iTX case. Compile, simplify. If you have 4 drives and want to add four more...move the data off the others to the horde. Then you have empty drives.
Think bro. If you have 2TB drives with data, they don't just float over to 3TB drives cleanly. They move of course...so keep it simple and just move it all over from the 2 into the 3.