Give us links to the versions. The madcow 5x5 which is so popular on here has an in-built confusion. Some of the exercises are down as 1x5 but are really a ramped 5x5. The other days which are down as 5x5 are a flat 5x5. For the 1x5 days, the top set will be higher than your 5x5 days and you take 5 sets to reach it.
Rest as long as you need to rest to be able to get the next set in but don't be lazy about it. As a general guideline, 1.5 to two minutes is typical during early weeks, rising to 3 to 5 minutes during later weeks.
dfht is pretty brutal. It's impossible to answer your last question without more history. If you're fairly new to this type of lifting then the Single Factor might be better for you at this stage than the Dual Factor. If you are experienced then there's no problem with what you outline. A guideline for starting dfht that I've seen is that you can squat 2x bodyweight.