Here are a few general tips to help you with your 1:43 kits.

1. Intake trumpets is one area that white metal can not replicate well. There are aftermarket items but these can get expensive ,especially if you are doing a V-12. If you can afford them I say go for the aftermarket stuff

In computers there is a chip socket that is soldered onto circuit boards. You can find these sockets at dedicated electronic stores. Make sure they are round sockets as there are other types. I placed the socket in a oven to soften the plastic then popped (or pried) them out. One socket has over 50 of these items. These will look a lot better than white metal ones and won't kill your budget

2. For white metal wings if possible replace the endplates with sheet brass for a more scale appearance. Use the kit part as a template for cutting the brass. If you don't want to do this you could file the entire white metal endplates thinner. Once this is done you can then file the edges even thinner to sort of fool the eye.

3. For white metal mirrors the stem is a very weak point. You should cut this off and replace this with brass rod. Once painted it will be more to scale and it will be a lot stronger and will resist breaking.
a/ cut off kit stem
b/ clean up remaining stem and mark location for drilling. It is recommended that you do this with the tip of an X-Acto blade. This will also help the drill bit from slipping when you start the drilling process
c/ Drill at the same angle as the stem before you cut it off. Use the smallest drill bit possible for the smallest brass rod you have. During drilling check the depth every so often. Make sure you don't drill through to the end or come out one of the sides. Depth of the hole should be at least 1/16"(2mm). Any shallower and the rod might not hold
Use about 1/2"(13mm) of rod. This is too long for the model but this will allow you to hold the part for painting gluing etc. Test fit the rod to make sure it fits in. Use a small amount of CA glue on the tip. If you use too much and it oozes out juts wipe away the excess. When the CA has dried completely check again to make sure the area is clean. Bend the rod if necessary. Test fit on the model before painting

4. Mount your finished model to a base. Any base. This will prevent handling of the model which in this scale can cause a lot of damage to wheels, mirrors, wings, decals etc. I generally make a spacer for underneath the car and use strong double sided tape to hold it on. This also helps give the car an even ride height.

5. Air Scoops, Brake ducts, vents etc. Limitations to the moulding process means that recessed areas of kits are shallow. With the right tools you can deepen these to make them look more realistic. I generally use a dental grinding bit and my Dremel tool. These are very tiny bits I get from my dentist. The recess does not have to be deepened too much. You only have to do it enough then add some black paint to get a more realistic depth. With any motor tool you have to be careful that you have firm control of your tool or it may run out of your hole and damage the part you are working on.

6. Drill mounting holes. Some earlier kits do not mention that you should drill out holes for where the suspension mounts. Always test fit as much of the suspension parts as you can before painting. There is nothing more frustrating then trying to fit suspension parts on and damaging the paint on the model or suspension parts.

7. Drill out exhaust pipe ends or replace them with tubing (brass or aluminum)

8. For priming a white metal body I use automotive primer or primer for metal. The brand I use for white metal and resin is Plasti-kote Sandable primer

9. Count your parts. 1:43 kits are generally harder to get than plastic kits and the majority of manufacturers are still classified as cottage industry. Since the majority of people who buy the kits do not start them right away it is wise to go through the kit completely to make sure everything is there. Better to do it now then several years later when the kit may no longer be produced. Not really a building tip but something I think everyone should do.

10. Most 1:43 kits come with a screw to mount the bottom pan to the body. I generally pre-drill the hole before using the screw. This can prevent to possibility of cracking the resin or white metal. You also have to be careful that you do not accidentally screw the screw right through the top of your model.

11. For mirrors most people will polish up the white metal or paint the surface a silver colour. In hobby stores there is some polished aluminum sheet that is thicker than aluminum foil and can be cut to shape. This has a very shiny surface and is relatively quick to do. In a pinch aluminum foil can be used.

12. the antenna that comes with the kits are generally large white metal items or flat photo etched items. Replace these with the fine wire. You can paint these flay black or use a permanent marker.

13. Some photo etched suspension arms are flat or do not look right. Some you can replace with brass rod. Ones that are supposed to be aerofoil shape can benefit from some filing of the leading and trailing edge. Note that this is note easy to do so I would recommend this to those who have worked with photo etched items before.