There are no hard and fast rules as dogs coats vary greatly. Show type have much fuller coats than workers for instance.
I have 2 show type and they are completely different
A puppy coat shouldn't need what I would call a full groom but Bailey is a fluff monster and her feet were HUGE so I took her to the groomers at about 4/5 months mainly so she would get used to going there and it would be familiar to her. I just got them to bath her and just trim her feet the first couple of times.
She has just turned 1 and is going to the groomers again on Friday. The only sad part is once she had her first proper groom although it was a lovely cocker cut, she didn't look like a puppy anymore.
My Jazz is just 2 and if I let her go more than 8 weeks between grooming she starts to resemble a poodle on a bad day
she has a really curly coat and very curly ears where as Bailey's are very long but much straighter.
It also depends on how you would like him groomed as hand stripping is different to clipping and you can't really do both. Both of mine are clipped but I don't show or anything they are just pets.
Brushing everyday is a good start to get him used to being groomed so a trim to his feet would be fine to start with I think. Owners also vary greatly in how they like their dogs to look according to time available etc.
Just go with what you think is best. Good Luck