No new way to level to my knowledge. Therefore, leveling is the same as in previous seasons. As for builds... the only that matters is GR20 builds, and fst_d3 recently added all those for season 11 on his website:
Completely random. Especially rifts it comes down to: RNG, what kind of rifts you get, what items you find, how well you know the low-level abilities of your classes, how well you play your classes, how much time it takes you in between, and in general just speed and picking the right difficulty (basically always stay on hard, many people make the mistake of going too high).
3-4 hours maybe? The fastest rifting 4 player group I know did it in a bit more than 2 hours but those were like absolute top players that practiced a lot. So aiming for 3-4 hours is a good time for a 2 player group with some basic planning. Depends on the classes as well of course.