Once burnt, yes, safe greenhouse gas. At least, no worse than any other combustion products. I mean, it would be nice if hydrogen wasn't such a pain, but we have to work with the universe we are given.
Methane leaks need to be contained to the amount practical, but they are doing that.
SpaceX has completed their mishap report, which states what they believe are the required corrective actions, actions which, it can likely be assumed, they have already completed. So all that is needed, from their standpoint, is for the FAA to accept their report, accept their corrective actions, accept the actions as done, and issue the launch license.
FAA could, however, decide against any of those things - that the report hasn't covered something, that other actions are required, that the actions haven't been properly done.
This is entirely in line with everything that both FAA and SpaceX have said.
I, too, love the idea of a wet workshop, but I see the problems. Mostly, tanks don't need micrometeriod shielding and insulation, and weight-efficient shielding and insulation would not survive launch. The kind of protection you'd need to add would easily double the mass of the empty tank, or you'd have to somehow wrap the tank in space. The reward is enormous amounts of habitable volume, but I can't see the cost.
They can't dig a trench. The water table is often above the natural ground level, and their pads are only a few feet above that. When starship dug that hole, water seeped in and partially filled it!
But it is the same thing at the cape - but there they brought in soil and built up the land by something like 10 meters, and built their pads and trenches in that. Moving in that much dirt would take years.
No. It is part of the space treaty that most nations have signed up to, that any part of a space craft remains the property of whoever launched it, and clean-up of it is the responsibility of the country from which it is launched.