RE: ML server...
Hi,
...I'm a little confused by your comments, especially the parts about the air being your main machine and thus being limited by the storage capacity on the air... To me, this implies that you would be using the MBA as the server, but you initially state that you want to convert the Mac mini to ML server (you can actually run ML server on both machines since purchasing OS X Server at $20 allows you to download as many copies/licenses as you have machines in your Apple ID). If the MM is the server, then the storage space on the MBA does not matter as much and won't be a limiting factor since any large hard disks (for iTunes, iPhoto, iMovie, backups) would be hung off the MM with the MBA gaining access to them through File Sharing. Thus this would actually allow the MBA to have a minimum amount stored on it (no large iTunes Library, no wiki sites, no mail, for instance)...
In my personal opinion, and this is what I do at my home, I would install ML OS X Server on the Mac mini and use the MM as the actual server for your home, not the other way around. The MM then runs Calendar, Contacts, File Sharing (AFP/SMB/NFS for any share points on shared disk filesystems), Mail, Messages (i.e., runs your own jabber video conferencing server instead of using the public ones), Open Directory (for network logins), VPN (allowing you to VPN tunnel into your LAN from anywhere in the world), and even Websites and Wiki (if you wish to post your own personal websites or wiki on the Internet) servers and Pushes everything to all of your other machines (MBA, iPhone, iPad, iPod Touch, other computers). You can use your MBA with Screen Sharing to manage your MM server from anywhere in the world so your MM no longer needs a monitor, keyboard, or mouse. Your MM also runs 24/7 and never sleeps (I believe it only uses 13W of power when idle) so your servers, including your Calendar, Contacts, Internet websites and wiki, are available to the Internet 24/7. You can also VPN into your LAN with your MBA from anywhere on the Internet. The MM also runs iTunes and you share its Library allowing your MBA and any of your other computers to access your iTunes Library including photos from your iPhoto Library with all computers. Any large disks, such as a RAID system, is mounted on the MM but with File Sharing the MBA has access to it. I do this wirelessly, including streaming HD video from the MM, to several laptops in the home, without any wireless troubles. I do, however, have a Time Capsule that acts as my wireless router and serves the laptops as hourly, wireless Time Machine backups. I don't know if your plan was to use the MBA as the wireless router, but I would recommend getting a different wireless router, such as the Airport Extreme Base Station or the Time Capsule (if you want both a wireless router as well as wireless backup to the NAS in the TC). Now you could get the Airport Express to serve as your wireless router, but since its ethernet connection is slower that the AEB's or TC's ethernet, you might experience a bandwidth bottleneck from the AX's ethernet connection to your Cable Modem (ISP). The AX is also smaller (which is nice at one level) and thus I suspect has a more limited wireless range than the AEB or TC. I actually also have an AX that I use to extend the wireless range of my TC router so that I have wireless outside the house in the backyard.
...just my two cents worth of free advice...and the quality of what you get is what you pay for it...
Regards,
Switon