I'm going to buy some Ikea Havsta cabinets (white painted pine) and hack a few together to make a full-wall (16' long) built-in.

My hacks will be some trim pieces between them and some extra shelving above, to bring them up to the 8' ceiling.

They are already painted white, but it's kind-of a white-washy paint, and you can see some of the wood grain if you look closely. It's not something I can or care to duplicate on the trim, I just want a solid white. So I guess I have to paint the whole kit and caboodle.

Question 1: I'm thinking it would be simplest to paint all the IKEA pieces before I assemble them, because then it's just boards, without nooks and crannies to worry about. Correct?

Question 2: Is there prep I need to do to the IKEA stuff before painting?

Question 3: Should I poly them after painting for durability? Product recommendations?