IDW version of Jihaxus

[minion]

Even the best paints and sealant/varnish won't stop joint wear.

If you want to reduce/eliminate joint wear than you'll need to sand down the joint areas and anwhere that'll rub as it moves. This reduces the surface level so there is more clearance between the joints and moving parts, especially after paint has been applied.
Easiest way to do this is to take toys apart.

For painting itself, I find any good model paints are usually fine. I myself have always used Citadel paints from Gamesworkshop but I know a lot of customisers who also swear by Testors as well as other brands.

Look forward to seeing him finished.