Hi Jordan !
Happy to see you on the community forum !
to answer you question :
1) the fascia is a projection of your mesh over your muscle/skeleton model, you can keep the head en the leg/hand but for the begining I strongly recommand to you to cut them.
to build the fat you will have to first project the fascia over the muscle, retopo if it's necessary (I strongly recommand that to get less polygon on you fascia than you mesh), the reproj the fascia over the skin mesh and combine and close the holes.
2) you can sim the fascia and the skin on the same layer, the skin is a zCloth and the fat a Ztissue. When you start a new asset I can recommand you to sim them separatly because the fat sim is pretty slow (much more faster than before !!!)
2 bis) you don't have to sim the fascia anymore, since the 1.3 or 1.4, I don't remember, now you can add pressure directly on a zTissue.
3) you will have to check if the animation is working like reality and taking care of the volume of the muscle and to avoid every wrong movement like the arm who go trought the body etc... then their is different way to drive you muscle system after the animation, Andy explain that on a tutorial, how to make a run up... their is every information about that on the forum 😃
good luck