Welcome to Champdogs:)
What was the friend of a friend feeding the pup before you took it on, and how often? I think it's common amongst most breeds to be feeding four meals a day to start with for a pup of about eight weeks, reducing gradually to two meals by about six months, but I am generalising. There are lots of lab people around who can be more specific.
If you do a search on here for house training you'll find loads of advice. One thing I would suggest though is not to play with him when you're taking him out to "perform" because you want him to know what you're expecting of him when you tell him "do your business" or whatever command you'll use. Take him out and be calm, give the command, and if he obliges, then loads of praise. If you have to get up to him in the middle of the night the last thing you'll feel like is a half-hour romp in the garden before he gets round to doing anything!

Good luck with your pup.
LynnT