There's a few questions in here... I'll answer some to start, but let me know where else I can fill in gaps.

This document is what I like to share that contains a wealth of information on boundaries. Feel free to browse.

https://johndeere.widen.net/s/mffgtzlwg5/create_use_boundaries_guide

Autonomy Capable boundaries can be recorded with a 7000 or 7500. They can be recorded using RTK or SF-RTK.

My head is spinning a bit thinking about the complexity of switching back and forth between correction sources at will. Best to pick one and stick with it consistently.

Trees are going to be a learning experience. The truth is, there are many boundaries today that were recorded near trees that are not very good.  But currently, an operator has always been there to take over when a boundary may be wandering because it was recorded with a lot of tree line interference. When there isn't an operator there, the standards for accuracy and quality go up, since there is no one there to lend a hand when the system can't. So there's a few options... chainsaw or farm the field manually doing the headlands near the trees for example and then letting autonomy do the rest.