To answer your last question first, no, many people going the bespoke route opt for button fly. I never would, as I think it is less dressy. I also simply don't like them. As for trouser closure, every tailor has a different way he likes to do it. I have many that I like very much: 1. On an Alan Flusser bespoke suit, trousers for braces, no belt loops. The trousers just have the two metal hooks, one at the top of the fly, and the other at the end of the rectangular bit of fabric that extends beyond. I like this very much, very simple, no buttons, fits great. 2. The second one that I like is on the opposite end of the spectrum. It's all buttons (aside from the zipper fly of course.) It's a top of the line Canali, really nice, Super 120s. I'm not sure how to descirbe the closure... There is no visible button closure, it's just flat around the waistband. However, underneath the waistband is a flap of fabric with a buttonhole in it. It's not just your standard buttonhole with a bit of fabrice covering it over, but actually this seaparate flap with a buttonhole in it. That does up at the top of the zipper. So, it looks like a pair of trousers with the metal tab closure, but actually buttons. And then, like on the Flusser, there's a fabric bit that extends further down the waistline, where it buttons (visibly.) 3. The final closure I like very much. It's on an Italian Brooks Brothers I have. the waistband closure is pretty standard - metal tab at the top of the zipper, and visible buttoning of the lextended fabric bit. It's the inside that I like very much - you know that button you do up on the inside just to hold everything together (sort of like the hidden button on a DB jacket?) Well, this has two. And the buttonholes are all handmade, and it just gives so much pleasure to button those up. It really holds the trousers in place, and just feels that much more snug and perfect than in my trousers with a single button. i really don't think I've described this one well, so I'll take a picture of what I mean.
Anyway, there's lots of ways to do it,and the more interesting the better, in my opinion. At this point, I'm probably never getting suit trousers with belt loops again. Braces, double pleats, side tabs. And I do like the Brooks double-button inner closure very much, so I may have to start asking for that. Best, ZJ