A 27 gauge 1/2 is fine for quads because there is very little fat covering that muscle but a 27 gauge 1/2 is too short for glutes (unless you are pre-contest shredded).
I would use a 27 gauge 1' or 1.5' for glutes. Otherwise the needle won't get deep enough to inject into the muscle. You will be injecting into the fat otherwise and can risk getting an abscess that way.
27 or 25 gauge 1' is very versatile. That's what I would order.
trying to squeeze oil through skinny needles is a pain + if you aren't getting the needle into the muscle you will end up getting abscesses. not the end of the world but the standard is 25G 1 inch for oils
if you are doing 1/2CC or 1CC injections once a week or something I see no problem with using skinnier needles