It looks great and if you used rustoleum flat black enamel that should actually withstand pretty well depending on your primer. Since it's actually a primer itself, it should be stronger than regular paint would and if you laid it on thick it should be fine unless your undercoat does not adhere to metal too well.
Trick with clear coat is thin layer(S)(plural). That speckled look you got will go away as the coat is laid on EVENLY. Ideally since it's a finish you want to shoot from straight above so it doesn't run, but if your rattle skills are up to par your light coats should enable you to get it angled without having to sand/wetsand in the long run. Overspray all day!!! if you stop the can (change directions) you get deposits/runs.
I use the primer route too though quite often and find it to be durable and effective. Also easier to reshoot later. Keep up good work I like the new look much better!