yes and yes.
it will rub the paint off, and it wont be the best stopping power..
im using this hub laced up by a local bike shop
Front Hub - Single Disc Black - Cycles U.S. LLC/Choppers U.S.
would be nice to keep that blue rim from the cranook and disc/drum hub.
it gets pricey stopping without pads on the rim and custom looks.. but worth it!
just FYI front disc brake without rear brakes can be tricky especially on hard fast stops.
my next bike will have full disc and front suspension, couldnt ask for more