Re: hub adapter vs spoke clamp
sprocket adapter sare definitely worth the investment imo compared to rag joints.
as far as that chain idler, 2 people gave me tips in that, did both of em and mine is rock solid, not slipping any where.
first hammer the 2 plates to be somewhat flattened, this will allow those plates to contour to your specific bike frame, rather then the generic shape they come with.
next eat a can of corn or some soup, hold on to the tin can, cut that up and make shims with it, place the shims between the idler mounts and frame and tighten it down. i set the shims in mine so the grooves from the can were vertical on the bike, like if i was holding the can sideways, hope that explanation works for ya.
lastly bring 1 of the other bolts to a hardware store, get nicer bolts about 1/4 inch longer, the other ones are junk and it mite be hard to make em reach with the slightly flattened plates, tighten them up and hit it with a hammer, bet it wont go anywhere, mine didn't.