I used a black elastic, it's comfortable and invisible, you can use a white one if you want something more accurate.
Since it's a delicate and narrow part I preferred not to weaken it by drilling holes, so I glued a snap plate on the inside just like on the rest of the armor. If you want total accuracy you go with the two visible snaps.
The drop boxes were, well, boxes, so they were closed on the back. I'll suggest white elastic to hold them, so it can stretch a bit and not stress the belt.
Yes, a black belt with black elastics to hold the thighs. The shins are held in position by the boots only, no strapping there.
If I remember well it was all elastic, no webbing anywhere, right Paul?