>>9723500I haven't painted anything myself yet. However, I'm also into Mythic Legions, and the customizing subgroup to that line is huge!
This guy has a ton of videos on customizing, and he even works for the Four Horsemen.
https://www.youtube.com/c/MythicCustomsThis video has a shopping list for stuff to get...
https://youtu.be/rqRqDeM9GVwand he recommends this box set of Vallejo Acrylic paint. You don't want enamel paint to go onto plastic toys.
Hope this helps you get started. You could also get on MOTU forums and ask them how they customize stuff.