Sure but after a few decades of packing we'd eventually end up with a direct democracy where every adult citizen is a Supreme Court justice and the legislative branch would be sidestepped entirely. Seems better than our current system IMO.
Yes, but each time diluting the power of the justices individually. Right now if you have one wacko justice who decides on the basis of political ideology instead of some of the established legal theories they have 11% of a say in things. Add another few justices who are relatively normal and the ability of the wacko to swing things into dangerous territory goes down. Even if the tit-for-tat tries to cram more wackos in you have to try to convince the Senate to let more and more obviously terribly choices through.
Yeah, same with ending filibuster and other speculated tactics. I don't think you can close the door behind you without a constitutional amendment, which won't happen.