Done. Some questions are a bit vague though. Like the hub, what size, well made? cheaply made? all different factors. Same with the frame/chain question- it depends on how you're planning to make it.
Yeah they're worth it, they stop the pads wearing at funny angles(if set up right), yeah I've used them, and yes- any material will fit but some may need to be trimmed for some backings.
Best/safe(st) way would be to buy a bolt on sprocket, but that obviously costs money. Will be worth it though when you don't eat shit on a hard downstroke. EDIT: IF your hub has a disk mount. If not, there aren't any brilliant ways to do it.