All great questions, Modochi. I'll try to answer some of these the best I can.
1 - I'm having trouble replicating this. Using a random rocky planet placed ~1AU from the Sun, with surface pressure ~1.0 bar, I don't see greenhouse effects anywhere near that high. Can you give a step-by-step process for getting these values? That will help us a lot in seeing where the issue is.
2 - We're working on some improvements to this. The issue comes down to performance. While the collisions can calculate and conserve the correct mass, it can be lost from the performance system culling fragments and particles, which is why you see some things shrinking and disappearing. We agree there is a lot of room for making this better, though a perfect solution is tricky.
3 - Thanks for the feedback on this. The idea was to make it easier to use Launch to put things into orbit around another object, to mirror the functionality in VR. I think this needs tweaking to make more sense on desktop, though. Regardless, the functionality should be the same as before if you toggle the Auto Launch Velocity right below the Launch button (Velocity can be manually set below that).