1- Just give the primer a light sand before applying the top coat. It won't be thick unless u plaster your model with the stuff! A light coat with a couple of heavier ones is fine, although u may notice mold lines that need removing, in which case u will need to sand these then apply more primer.
2- ???
3- Now correct me if i'm wrong but as far as i know your Tamiya Silvia shares alot of its chassis parts with the 180sx. I did one some years ago and now completely reworking it but these pics show what i did;
Lowering the front i quite simple, just remove the top of the front springs and rebuild the locator pin from a piece of plastic rod or stretched sprue. You will also need to extend the connector for the steering arm. Mine was more of an experiment in completly rebuilding the suspension with reals springs, but there is no real need to go to such trouble.
You will also need to add a spacer for your now shortened spring.
I never lowered the rear when i first built this, but the simplest way to lower this complex set up is to remove the horseshoe shaped locator for the hubs. Cut this away and then you can simply glue the hub further up but take care with positioning it right or you will end up with a wheel off the ground.
4- Painting the inside looks alot better.
5- Thats up to you? Personally i prefer to prime everything for a better finish and i would recommend you to do so too.
