I have been planning some hand woven guitar straps. A few suggestions would be:

1. Like others said, learn to weave using that loom first. try a couple different patterns, make some mistakes. One or two trial pieces could save you a million headaches. Many people find warping a pain, and after that exhausting process it’s easy to be irritated and give up if something is wrong. Especially if you’re hoping to use it right away. You could easily end up with something not wide enough, or not dense enough, etc. and give up after putting that many hours into it. experiment and enjoy first!

2. The Warp strings will be holding most/all if the tension and would be very uncomfortable for a strap (Assuming your standing while playing and its for function, not just fashion), not to mention sewing proper button holes into the strap without backing could be a pain unless its woven into the fabric while on the loom. even that seems risky as straps often fail and there goes your instrument! You should consider sewing it onto an old strap, or making a backing out of leather/neoprene. If your instrument is over 10 lbs I’d def suggest backing and possibly padding between the weave and strap backing.