Personally (with a nice 780 literally on-board), I would get a nice new roomy tower case. Not that the 630i case wouldn't do, but IMO it lacks some of the nicer features that new cases provide, such as better options for cable management, and side/back panel cut-outs so you can easily add CPU coolers with little fuss.
With a 780, you're probably going to want at least an 850W PSU--any solid rated Corsair or Seasonic one will do the trick, with modular ones giving you a cleaner PC interior (if you don't need all the cables it offers).
As for the mobo, I've been recommending the ASRock Z87 Extreme4 (link below), but again, any solid-rated (by newegg.com customers) ASRock, Gigabyte, ASUS, or MSI board should do the trick.http://www.newegg.com/Product/Product.a ... 6813157369
Here's another mobo suggestion (Gigabyte):http://www.newegg.com/Product/Product.a ... 6813128591
Note that these newer mobos require an 1150-socket Intel CPU (not the Intel 1155). However, all CPU coolers from the 1155 series work fine with the 1150 sockets, so no problem there. Also, if you go with an ASUS mobo, note that it requires a modification to the front panel connectors; ASRock, Gigabyte and MSI mobos do not require this mod.
Re: the extension; I'm clueless on that one--I'll leave that for our gurus or anyone who can answer it.