I'm no expert but I've done several sets of wheels, car bumpers, mirrors etc and can achieve a near perfect finish. I'll ramble on with some of what I've learned though trial and error.
It is all about prep, if you can do the prep the bodyshop will paint it for a lot lot less. I mean if you turn up, in primer all ready they just have to spray it a few times and hand it back, they'll do it for beer!
The real issue is that it is dangerous and hard to use the 2K / pack paints at home, it can kill you but of course it is much harder than the solvent based paint you get in the normal aerosol.That said it is not impossible to get a couple of years out of these can jobs. You can now buy 2k in a can with the activator in a special capsule, the jury is out on if/how dangerous this is an what precuations you need to take.
While the below pics are wheels, not a bike, they were my winter wheels with snow tyres. I drove them six months this winter in all conditions and they still look like that now. The only issue I had was some paint chipping on the centre hole where they hooked up the wheel balance machine but that was maybe due to the paint not being fully hard. You really need to allow a month at room temp for all the solvent to escape and the paint to get hard. I'm not sure baking it helps, I've yet to paint anything that would fit in the oven or I'd of tried it :p Heating the cans before spraying helps quite a lot, you increase the pressure for sure so be careful but it flows nicely if its been sat on the radiator for 20 mins!
There is a lot of talk on how to paint but people get carried away with sanding once the colour is on or inbetween laqcuer coats; there is no need. 90% of the sanding is done before the colour lands. You should always apply some heat, I'm using one of those cheap panel heater things, if you can see the paint sagging like its about to run you can hold the heater close and it will stop. Don't forget that paints shrinks when drying so small imperfections in terms of too much paint often disappear once dry.
Fill any damage with metal bodyfiller (isopon metallik), then a coat of etch primer, follwed by two or three of primer or filler primer.
Sand this out this to perfection, if you are going to put any effort into this job now is the time, get it perfect in primer and you won't need to sand again, any defect showing now will never ever get covered or go away. If you break through add more primer, bare metal will show in the finished job.
You should only dry sand the primer as it absorbs water, if you do wet sand leave it dry in a warm place for a few days. I'm using 320-400-600ish grit, you don't need finer. Many people say you can just sand to 200-300 grit but personally those marks always show through once I apply clear coat, so I go to 600.
Apply say three coats of colour, light first coat then build it up. It is very easy to try and get an even coat on the first coat, you must resist this temptation. If you have even coat on the first coat then you went too thick! It is easier to not get a run than it is to sand it out!
Remember that your paint probably requires a clear coat or lacquer which means you should not expect the base colour to look good, it will be slightly rough and matte...unless the texture is awful it will not be visible under the clear. Some metallics are pretty abrasive looking..
No matter what anyone says you cannot sand a metallic base coat, it is logic really, it contains metal flakes that must stand up at the surface, if you sand it then you will create a mottle, blotchy effect. If you have to sand then you must apply more paint afterward. You can sand flat colour but I have never needed to, if I did I would still apply another coat.
Clear coat or lacquer is the only time sensitive part, you should apply it no more than a few hours after the base. My approach is one very light coat, wait 5, another light-ish coat, wait 2-3 and progressively building up to say four coats. If you leave it dry too long it doesn't help, you want the previous coat to be tacky. Clear runs very very easily and it just happens, you don't always see it forming, it all looks great then bam! a massive bloody sag appears
I try to make the last coat as thick and wet as possible but it is not really needed, it just feels good for the ego. You are going to sand this next so the only important part is you have a decent overall thickness.
Once the clear is hard you need to wetsand it with 1500-2000 grit. Soapy water, keeping it well lubed and washed as you work. You just need to remove any orange peel, runs or debris. Of course this will seem like a crazy thing to do as you flat it off but you need to do it as this is what differentiates between most peoples rattle can jobs and the good ones. You can sand away for a very long time before breaking through the clear, watch out for corners, edges and rasied parts but you can probably sand for five minutes in one 8x8inch spot with 2000 grit and not go through; don't be too scared.
Once its nice and flat you need to polish it with G3 rubbing compound or similar. I have a DA buffer, small 4" pads and Menzerna polishes but this is because I like to polish cars, its not 100% needed for this task. Don't wax it for a month or so because the paint solvent needs to evap...
The wheel photos are all before wet sanding and buffing, the car bumper has been wetsanded and buffed hence the mirror finish. The wheels took two weeks but I did (stupidly) sand them back to bare metal rather than use paint stripper so a lot of time was wasted there
The bumper repair took two sessions of about 4 hours. (it was not meant to be perfect repair, its my teenage cousins beater car that she keeps ramming into things, I was only supposed to cover it up a bit but got carried away.
I've bought a 01 Kona Stuff thats going to get a candy apple paint job, I'll detail that as I do it over the coming weeks. I'm going to try to use 2k primers/clear in a can with an excellent mask, good ventilation and a lot of care. I'm hoping to gain that last little bit of toughness and longevity.