I know I didn't describe it well- can't find the exact video but most people I know sit In this spot to take out the nexus- when you jump down , head to the left. You can run back up on a incline that's off to the side of the main gaming platform if you will. It's from this spot that you can jump towards a cubby hole on your upper left hand side- there's like a cut out in the rocks in a high platform - once in there nexxus has a much harder time hitting you and you're practically impervious from ground attacks - hope this was of some help

Yes, just kill the minatour when he comes out. Always be checking and if you have a fireteam assign someone to handle him.

Yeah. A Minotaur spawns behind you if you stay up top too long. If you kill him. They will continue to spawn one by one.