this thread should probably be over in the resources and references section.
as for me, answering the question "what do I use to customize" is extremely difficult... I use almost EVERYTHING.
basics of what you've already gone through: acrylic paint, a multitude of fine tipped brushes, paint thinner, super glue, exacto knife... etc....
some of the not so common materials
hot glue gun, two part epoxy glue, silicone, two part resin plastic, modeling clay, apoxi sculpt self hardening modeling compound, fabrics, leather, etc...
tools:
eyeglass repair kit screwdrivers (ranging sizes), pocket knife, exacto/razor blade, vice grips, channel locks, needle nose pliers, wire cutters, soldering iron, siscors....
like I said... just about everything you could think of I use it...