Reddit mentions of Tamiya America, Inc Putty, Basic Type, TAM87053

I’ve got some modeling putty that gets the job done and I picked up a sandable filler primer for later. It shrinks a bit after it dries, so I’m probably going to have to pick up another tube of the stuff.

This is what I’m using

Keric has posted some great info but I would add a bit of extra info to that. Buy some gloss varnish so that the Decals look & stick properly. I would suggest using PVA wood glue to glue canopies & clear parts because it's better value for the money. Also, if you're doing any brush painting, buy Vallejo Model Colour paints. I've heard they brush paint the best.

Paint formatting chart to be used for obtaining the correct paints from Vallejo.

Use tweezers to handle the smallest parts. Thin the paints before you paint & Apply a few thin coats instead of one thick coat. I would suggest getting a bottle of modeling glue with a fine applicator nozzle or a brush to apply the glue more precisely. i advise you to keep a tube of plastic putty that's either water or solvent just in case you need to fill any gaps.

Would also suggest you join the Britmodeller or FSM forums for more advice:

http://www.britmodeller.com/
http://cs.finescale.com/fsm/f/default.aspx

More advice: Scale Model Guide Quick Kits
Guide on brush painting

ok thanks - so prime, fill, sand, then paint? is it this stuff?

How big are the gaps?

Anything bigger than 4-5mm I'd use Bondo.

Smaller than that, use Tamiya putty.