This is getting into some really deep and heady engineering, as well as some advanced rigging necessary, with further challenges of wood degradation rather rapidly because of the location.
Most of it sounds plausible (with caveats) yet without blueprints/CAD/diagrams it is hard to speculate beyond that.
The "load criteria" is not typical as it reads like you are going to be using round logs?
Allowable deflect is base on the "lumber species" but a set IBC standard.
As for #3...???...I could begin to go there without blueprints/CAD model to look at, perhaps others would venture there from just a verbal..
There are way more questions here than answers, at this time, for me. I am have concerns about "tree selection" mounting system, general design, decay issues, etc.
I will check later, and perhaps others would/could be of more assistance...