First Off, pull it all to bits

Grind off any extraneous lugs (no not yer ears), ye won't need to flatten welds unless they're really spikey. Powdercoat covers them nicely and ye won't weaken any joints.

Send/take it to then nice bloke wot does powdercoating and let him do his thang. Any good powder coater SHOULD put bolts (or in this case paper, not shite all over living room carpet) in the threaded holes, this keeps the powder out.

Marty's wheel in a fetching Blue

Marty realising that there's a bit more work to be done.

In this case some powder had got into the disc bolt holes, ye could tell coz when ye tried to put the bolts in they would go tight in about 2 turns.
Spray some WD-40 in the holes and gently! ream them with the correct size of tap, keeping it lubed and turning it out a few turns after every few turns in.