Q: paint and filler for plastic and resin

I'm extremly new to the whole prop building thing. As such I've decided to just start with learning how to finish the product first, then eventually move into creating it. I have two different items I'm working on but don't know what type of paints to use.

I have a resin item that I want to glue items to and paint to a silver metallic. I'm guessing I should prime it first then paint, but I don't know if there's a certain type of paint that typically works better, if I should affix the items, then prime, then paint, or prime and paint all the items seperately and then assemble...maybe it doesn't matter at all? I don't know the resin type, I didn't think to ask when I purchased it cause at the time I didn't know there were different types of resin...which may also not matter at all.

The other item I have is a plastic gun that I want to fill in the screw holes and then paint to a black metallic (the nose of the gun will be silver metallic). But...I don't know what to use to fill in the screw holes and also if there's a better paint brand/type/style to use for plastics.

Any advice is very much appreciated

Simply-
If you use a filler for this type of work try to only use the two part filler used in car body repair. Dont buy the fibreglass filled version, its only good for major repairs, get the basic stuff.
Mix it according to the instructions, Id do a test first as you are new, just to be sure !
Before putting the filler onto the model etc lightly sand the surrounding area to make sure the filler has a nice surface to stick to. Its stinks so again be careful! Put a fair bit on but dont overdo it, just enough to make the surface slightly proud.
Once hard sand it back with 80 grit going on to 360 grit sand paper.
As for painting and glueing, it normally is easier to paint things a different colour off the model first and then attach, if this is possible.
The best paints are the spray kind, again used in car body repair. Some art shops sell suitable paints in a can too, try the car stuff first( you will be in the same shop buying your filler anyway!!)
Lightly sand again. Use 240 to 360 grit sandpaper for working on the model, with 360 being the last paper before spraying primer. Use 40o to 600 grit paper between colours.
Spay and colour carefully, allowing time to dry between coats. little is better than lots, no matter how tempting it is to blat it all on in one go- it will stay soft for ages if you put to much on.
There are lots of glue to use: 2 part glues, superglues, contact etc, so its hard to say. resin to resin etc thick superglue is brilliant, 2 part glue is a little more fiddly but will give you more time to line things up ! Try to avoid glueing onto paint- scratch the paint off where you are glueing first.
Avoid working on PolyPropelene (PP) as hardly anything sticks to it !
have fun and post pics !!