KiaOra! Welcome to the forum!

1. You will need to get the neck straight before you go about your fret levelling. You need to get or make a notched straight edge that will allow you to gauge the straightness of the board without resting over the frets. From there you can get the frets levelled.

2. This is a matter of much conjecture, many do all of the woody working bits and grillage before colour and finish, some do it after.
I've done it both ways and I've no real preference, though some prefer to get the thing set up and playing right before they go through the drama of paint or stain etc.
Its really up to you, if you don't fancy the idea of trying to drill in a finished high gloss painted body, then get it done up front beforehand.