How many naps should my 7 week old have during the day, and about how long each time?

We have a pretty good night-time routine for Peter, but no real day-time routine. He used to just sleep whenever he wanted during the day but now that he is more 'awake', he resists sleep and I think he really needs our help to know when is nap time. I am just after some guidance about when and how long his naps would be appropriate.

Also, sometimes when we put him down during the day, he sleeps for AGES, like 3 hours- is this too long? Should I wake him up?

Thank you!!