anubis...apparently a lot of customizers use a very, very fine brush with the eyebrows.
There's a couple of DBZ Figuarts groups on Facebook you can join (DBZ Figuarts Rebirth USA, Figuarts Collectors, etc.), some customizers (including those that create new molded pieces and sell) frequent those boards and are always friendly when asked about tips. "Ferrytale Customs" (Fernando) is one of the best when it comes to repaints and work. He'll happily share some tips.
One thing a lot of them also do is create new hair pieces and offer them for sale. There's a couple of "fixed" Goku SSB molds that they've offered up that I bought. They're usually based on existing head mold with slight tweaks - they've mostly focused on Goku, Goku Black, and some Vegeta sprinkled in here-and-there. The work is REALLY good with superb paints. I've bought the Ferrytale's SSB mold (based on some of the images of Goku in the Whis outfit), the Ferrytale SSJ2 hair mold, and recently got the AJ Customs SSB mold (an adjusted SSB 2.0 mold made to be more accurate). Also got a transparent Full Power Broly hair piece.