I don't know ow this affects your decision but, I would get rid of the Coolermaster PSU. If it's from the family I'm thinking off I wouldn't want to have it running a server. So this gives you a good opportunity to make use of it in a appropriate situation. I had a Coolermaster 500 watt in my first PC build. It would cause all kinds of problems when I would game even though it should have had enough wattage. I've got a second hand one now that I wouldn't want to use on anything other than a low power build. The issue is that they are an older design. With a server you are interested in what they can put out on the 12V rail. In the case of those PSU's they can't put out very much at all. If you look at what is printed on the side of the PSU it should tell you what the 12V is rated at. My 600 watt Coolermaster should only be considered a 380 watt PSU by todays standards.
Like I said I don't know how this factors into the decision, but you don't want that PSU in your server. So this is your chance to make use of it. So if that means you don't have to look for a PSU for your brother maybe that will have an impact on the case choice. Good luck.