I don't know how far a high g will stretch.You are going up three whole tones, five semitones so it may be getting a bit tight and tetchy. Is there a prize for finding out seeing as you have posted this in the "Contest" section You may be better off in the Ukulele Tips, Tricks and Technique or Uke Talk section
I keep one of my ukuleles in D, which makes the g string an a, and that is pretty tight. Also, it will put extra stress on your bridge. Don't think I would try it, myself.
Yes. You'll be fine- especially for a change that miniscule.
"Thicker Gauged" strings are essentially just strings that would normally be elsewhere in your setup. For example, the high E of an 11s set? That's just a B string from a 9s set. Tutuapp9appsShowbox