1 - Behind the dash it tough. There's less room in there than you might initially think, especially when you consider the number of cables, motherboard mounting and so on. Make sure you have a backup plan.
2 - Your PCU has a max draw of 84w. That's a 7A draw on the 12v rail. Using a DSATX, that leaves 5A on the 12v rail for anything else (motherboard, HDD, monitor, etc). It's something to consider in your build.