[euromodder]

Forget the filler - it's where trouble starts all over again.
Grind the welds down, and leave it at that.

Use a rotating wire brush on what rust you can't cut out to get rid of as much rust as possible - that kinda paint helps, but it can't do miracles.

Degrease, prime & paint, then clear coat .
A decent quality automotive spray paint can will do.

When I repaired my crashed GSX750 m/c the spray paint I used (Motip) was better than what Suzuki put on in the first place !