Yeah, the slim motherboards that I was talking about are more rectangular than square. They usually only have 2 DIMM slots for RAM though, as opposed to the typical 4. I already have my CPU, an AMD A10-5800k, which is an FM2+ chipset. I have already found numerous boards that can use this.
As for watercooling the 750, I know it doesn't need it, but I wanted to set up the loop for a future water cooled card. I plan on upgrading to a 970 down the line, and wanted to be able to simply swap the cards out, without having to modify the lines. This is currently done purely for asthetics.
I haven't decided on the PSU yet, but I have seen some decent fully modular ones that are 600-650 watts. Seeing as how the new Maxwell architecture of the 900 series doesn't use up a lot of power, just like my 750, I really won't need a massive power supply for SLi'ing my cards.
Either way, this is still just an idea, and I haven't finalized anything. I know the case is tight, and airflow isn't the best. I'm still working on a few things, so we'll see what happens.