3 1/8" is what I think I went with. I'm not sure how to size. I'd just give them a call. I have a 5 1/2 k and h with an 8 " hi vis something or other in it right now. No issues.
I'm using the 6"-9" inch wedge holder. Mine holds 2 wedges and I haven't had a problem. I've been using it for about a week and a half while at work. It seems to keep them right where you need them. There products are very well made and thought out.
I don't but I think it would be a nice feature to have. Depends on the weight of your axe I suppose. My belt I wear is on the outside or over my chaps that have suspenders attached already.