Covers: I have Bummis Super Brights, Mother Ease Rikkis and Thirsties and I prefer the Thirsties, the Bummis come second for me. Many people love the ME Rikkis, but I don't. They seem to run quite large, too, so don't upsize too much.
I also have Wool Covers (Disana) for night time and love them. And a few home made ones for day time just cause they're cute. Am planning to either make or get my MIL to make some wool longies for winter.

Snappis: I love them with Terry flats and fitted Terries like Mandy Macs. I do now think that they kinda wreck bamboo terry, though. Not sure whether pins would do the same. I think 3-4 snappis will be enough for you initially. You only need a couple but they have a habit of disappearing temporarily so having 1 or 2 spares is a good idea. I never used pins as they seem more time consuming.

Flats: I used to rave about bamboo terry for the softness and absorbancy. I am now more dubious as I find they just don't last. Not sure whether it is just the quality of the ones I have or whether this problem exists across the board. I found they got very thin very quickly and develop little holes. I've only used them part time for about 6-7 months and I although I didn't expect them to last through multiple children, 6-7 months is not enough in my opinion, especially when considering the price. My cheap BigW cotton terries are still going great guns at a fraction of the cost. So i think if I did it all over again, I would buy good quality cotton terry instead.