Remodel with popcorn and orange peel

My girlfriend and I recently bought our first home and we are doing a medium sized remodel. Part of the process has involved tearing out some drywall (for plumbing, electric, etc.) and scrapping off popcorn ceilings. Currently the walls have an orange peel texture, which neither of us are a fan of, ideally we would like a skip trowel look throughout. We are going to be doing most of the work ourselves and a couple of questions have arisen with all of various surfaces.

1) On the ceilings after the popcorn came down the ceiling was taped well, what would be the least time intensive way to finish them? can we just paint a primer coat and be ready for the finish coat?

2) We have many places where new drywall butts directly against an orange peel textured existing wall, with the existing texture sitting around 1/16" higher than the new drywall. How do we mask this "drop."

3) As 90% of the walls still have the orange peel texture, without removing all of the drywall, what is the best way to turn orange peel texture to a skip trowel texture?

Thank you for your help!

Skip trowel over the orange peel. There is NO need to remove the drywall. There is almost no way to handle an offset like that unless you feather onto the lower sheet, but even then there is going to be a noticable dip when light strikes the wall the right way.