I just brushed it in, I do not have the time or money to make cores sadly.
I did these in a rush ( I should know better ) and they are slightly too thick in a couple of places and I had to repair them in 3 places, which does not bug me that much but they are way thicker than the left hand, and that does irk me.
I will do them again and take my time hopefully Tuesday.
EDIT : sorry didn't see 2nd question, im happy to answer anything if I can, I am told it is best to paint silicone within a week, preferably 48 hours, having said that the left hand I made went unpainted for over a month, and the paint is fine on it after countless showings to people and test fits etc.