It's very much like having children btw, I think - they're not equals...not because of dominance theory, but because you're in charge. (though once they know how to behave it gets a bit more equal)
I don't see any problem with letting him play in the garden - unless he's literally spending hours out there unsupervised or you're unhappy with what he's doing in the garden.
The 5 minutes rule...well firstly he's 5 months so you get 25 minutes, it's not a strict rule, if you go a bit over he'll be fine, if he's offlead snuffling about that doesn't count. It's enforced exercise, anything he can't or won't stop doing through choice and it's to do with building up muscles slowly and steadily to support joints, so there's no reason at all not to give him multiple walks as long as none of them are really long ones. (I have to give my dog lots of little walks because he has a joint problem, little and often doesn't allow the muscles to get too tired to support joints)
If you're worried about recall get a long line and practise it. (I know it's already been said)
Training now pays off massively, the more you can fit in the better and it'll help with the biting if you can actually give him something else to do rather than just expecting him to stop if you see what I mean...basically like suggesting an activity to a toddler who is doing something you don't want rather than just telling them to stop doing what they're doing.
Another thing to consider based on your last post...an hour is a fairly long time to be playing without a puppy getting overexcited, little and often is better...they get overstimulated and also overtired - again, like toddlers and that's when they commonly get bitey.
Basically, puppies are like furry toddlers, only instead of all the things a toddler does, they use teeth, when they're too excited, too tired, grumpy, happy, bored, anything else, lol. Except, they're so much easier to train than toddlers.
The barking at night, really you need to either ignore it or if that isn't an option then rethink your sleeping arrangements either with a view to gradually retraining him or just so that it's no longer an issue.