I agree with the divider crates. Too many people get a crate big enough for their 'adult' pup and then wonder why it carries on piddling and pooing everywhere. You can either buy a small, puppy crate and then a bigger crate (for adult size) when it's outgrown the puppy crate, or just go straight for one with a divider. That way, whilst pup is small you can reduce the size of the crate so it doesn't have room to go to the other end from the bed end to do its toileting. I should think you're looking at a 36" crate for a lab. I really like the DogHealth cages, they sell from their site or on e-Bay, not the very lightweight crate, but the galvanised ones which come with a divider as standard. But there are quite a number of other people doing crates with dividers now.
3 doors is good 'cause generally you get one on the long side and one each of the short sides, but one of the short ones lifts up ... I like lifty uppy ones, no crashing in open doors when I'm wandering around the kitchen in an early morning daze ....