With the white and yellow paints you need to undercoat them with a more opaque color first. Or you simply need to slowly build the paint up with watered down coats first. I stand by Vallejo paints. They are the best brushing paints in the business.
What color is the paint? Did you apply a clear coat on the first paint job? I would mask off the panel that needs to be retouched. But be careful how many layers of paint you add to touch it up. You'll need to do light coats to build a base and gradually return the spot to the same depth of color as the rest of the paint. If you put on too many coats you may have a piece of the car that looks uneven. And in that case you would need to respray a whole section of the body to blend the whole thing back together. If you sanded through clear coat on a metallic paint job just make sure you do light coats because spraying metallic paint over a clear coat on itself will tend to give it much more depth which can appear uneven. The section that you respray may end up looking like fresher paint than the rest of the car.
In my opinion OP it was the paint that caused your bleed through not the clear. I've had this issue with Duplicolor paints many times. It might have something to do with how heavy your coats are but you will get ghost lines and "bleed throughs" if you are not careful. I would use primer sealer on any body you want to paint with a duplicolor lacquer.
1500 is sufficient but I take it 3000 now because 3M has come out with a 3000grit sponge pad that makes sanding a whole lot easier. Testors metalizer is the very best paint to use if you are wanting to paint a car body silver. It's the only thing I've seen that truly matches an "in scale" grain for a 1.24 car body.
Here's a tamiya NSX i painted with aluminum metalizer non buffing. Primed with Zero primer and wetsanded with 3000 grit. Cleared with testors wetlook.
Metalizers are designed to be sprayed on bare plastic.
If you are priming the surface first you need to sand it down up to 2000-3000 grit or higher. The metalizer is an extremely fine grained silver. It will show any imperfection or paint (primer in this case) texture underneath it.
Honestly I just judge it by feel. If you've put on a couple of heavy color coats just let it gas out for a few days then apply clear. Waiting for weeks isn't necessary and I haven't had a problem with it.
The problem with ts-13 is that it is "hot". it can and will destroy decals. This is why wetlook clear maybe more suitable in that application.
For me personally. The joy in building is trying to do the best I can. I don't go all out with aftermarket parts and photo-etch but I definitely use ignition wires, fabricate my own hoses and seatbelt catches.
I've been building model cars for a long time now. The one lesson that has made the biggest difference in my modelling is this. You have to treat the model like a work of art. Secondly you need to give yourself the leisure and time to do the best you can.
It's like anything else. You can't just magically rush it and expect it to look good. You don't hand paint an engine with silver because you know good and well it'll clog up detail, show brush strokes and look like a mess. No, what you do is research photos of this engine online. Then with your experience of paints determine what would best represent the texture of that block. Smooth engine surfaces are best replicated with MM aluminum metalizer. Rough texture= Tamiya XF-16.
You have to simply change the way you view the model. Expect more of yourself. If you make a mistake, do it over again. Even if you have to strip something in brake fluid. If you want perfection you have to strive for it.
Also another thing. There is no substitute for quality tools and supplys. If you want to get serious about modelling. Buy an airbrush and buy a good one that'll last a long time. Don't even waste your time with cheap plastic ones. Iwata is amazing here. This is the same for paints. I'll save a lot of people some trouble here. Paint your interiors with acrylic paints. Vallejo is the best by far for this. Their brush paints do not leave brush strokes and dry evenly. Their airbrush line is fantastic too. Their colors are very opaque as well.
For me its like this. Bodies=Tamiya/MM/Zero/Testors One coat. Engines=Tamiya acrylic/MM Metalizers/Vallejo. Interiors=Vallejo. Brush Paint details=Vallejo.
I also find that painting areas of the model that are hidden on final assembly helps reiterate to myself that this is a piece of art. Sure I might waste a little more paint. But I know that I painted those areas when it's all said in done. And I know that if I were to do a photo shoot with just chassis it would look extremely neat.
Lastly. As i said before do not rush anything. If you are not giving yourself the time to strategize, research, and do your best work you will simply not accomplish it. I may never enter a model competition because I know my best means going at my own pace.
Planning is key to this hobby as well and it all ties in with patience. If you have a curbside engine with molded in detail for example. The inexperienced modeller would try to brush paint those details. He may or may not do a fine job. But the expert will carefully mask those areas with tape. He'll airbrush parts he knows he can't paint with a brush. Then he'll mix a few acrylic colors to a shade he likes, dilute the mixture and begin shading highlighting areas of the engine bay with a brush.
In regards to how much detail I put on a model I judge by outside appearances. If the body does not match photos of the real car it must be modified and fixed. This is regards to panel lines mostly. Some kits are engineered to have separate body parts where on the actual car the panels are a whole piece. The tamiya XJ220 is a good example here.
I try to achieve details I can reasonably do and replicate to give the appearance of complete accuracy from an outside glance.
I started a thread on automotive forums a long time ago discussing the colors for the xj220 and long time member told me what they were. JD3 is Silverstone and JD4 was the monza red. They were exclusive colors for the xj220 so they are very hard to find. I basically just tried to find automotive touch up websites that might have that code and lucked out on one. The paint is on the way so i may have the right color but only a test will tell me how small the flakes are. Im pretty sure it's a pearl color so it should look like it's in scale.
I would imagine JS0003 is quite similar but I guess we shall see. Hoping to make my XJ220 as good as yours! I've been going back in forth on mine for a while now. Wanted to do one in silver for the longest time but last week I though the green be a more fun, more unique choice.