The biggest thing in my opinion is to really prepare yourself for all the variables that could pop up and throw you and your crew for a loop. Pre-production will save you once production starts. Stay organized throughout the entire production and it will save you time in the long run.
Editor - It depends on your preference as well as the editor's preference. Sometimes he/she likes to be on set during production and sometimes not. That is something and the editor need to decide together.
Post sound - Have a dedicated sound guy & boom op to record the best possible sound on set. More than likely you''ll have to ADR some stuff in post production but it's crucial to get the best sound as possible from the get-go.
Composer - Get a composer on board at the beginning so when you have a rough cut to send, he/she can start putting together a cue list and some rough tracks. Definitely collaborate as much as possible so you both are on the same page.
Promotion - You don't want to release a trailer too far in advance. I always was told around 1 month before the movie is to be finished. It's nice to create some buzz before the movie is released but if you do it too far in advance it can fizz out. This is ultimately up to you! I think networking and word of mouth is always a plus.