NB [# 3] that's just a 5mm Riv nut; fit mudguards maybe , not brake center bolts....

Rust on parts your issue?, take them apart paint the rusty ones,
put it back together , put in new pad inserts...


Or,
Go with a Mini-V , long enough to clear the tire, brakes,
or convert to proper V brakes..



Avid ultimate cantilever brakes are certainty pretty..



there are others..; Pauls comp




....