With a 23 guage it will take a little longer to push the oil through, but it will work fine. As far as the length, 1" is good for quads, and shoulders, you can use it for glutes if your your bf% is relatively low.
I have used 23 1" for My glutes with no problem, Unless you have a big fat ass, 1" will do. It does take awhile to draw the sust with a 23cc pin but it will do the job. As far as a 2" needle goes, I would never put that near my ass, 1.5" is the maximum for me