Reddit mentions of Lenovo Microsoft MCE Media Center Remote Control USB IR Receiver RC6 KIT

the idea with kodi (XBMC has been renamed) is that the user interface allows for opening those files via remote (another example), in a way that is easy to do from the couch. Hence a high wife acceptance factor. And since Kodi can be installed on a cheap android stick, apps can sit alongside your PC's saved content. example

Some other UI's

Excellent build. I have nearly identical requirements to you and my rig is very similar to yours.

The processor I used was the A8-3870k (it was cheaper for me than the 3850 in Canada) and I went with a micro ATX setup because the case of my choice was mATX.

You will have no problems with that processor. It's simply a monster. Plays and processes flawlessly. XBMC runs perfect. I've got my OS and programs on a 120GB SSD so everything is snappy!

1. For the SSD mounting, you can pick up adapters for less than $10 that let you mount them into standard 3.5" bays. However, someone above mentioned using velcro which is a simple alternative and should work fine.
   
   
2. Wifi cards are a dime a dozen nowadays so you'll probably have to get a standard card. Just get one that's wireless n compatible with a solid speed (you can get a wireless n 300 Mbps card for about $30). Your router may not even be that fast so you can adjust accordingly.
   
   
3. I know you said you didn't want a keyboard/mouse but this one is really good I swear: [Logitech K400] (http://www.amazon.com/Logitech-Wireless-Keyboard-Multi-Touch-920-003070/dp/B005DKZTMG). It looks nice and is very useful. You'll need a keyboard whenever you need to tweak things or use the web browser so this thing is great.
   
   I have the K400 and also a cheap [MCE remote] (http://www.amazon.com/Lenovo-Microsoft-Center-Control-Receiver/sim/B006TPPVKE/2) which is great for non-tech savvy people in my house.
   
   
   Overall I think you'll be very pleased with that build. Have fun!