Hi there and welcome to BW
Starting EASY - all you need to know and more!I would start by just doing what you usually do and observe for three days, record the E times, A times and S times. Remember A is any activity when LO is awake, where nappy changing or eating. Also record the morning WU time, the BT and and any NWs. Try to make a short note of if he needs resettling at naps or if he was reluctant to take a nap. After 3 days you should be able to see a pattern form and go from there.
I'm guessing he is BF as you say he feeds for 10 mins, some BF babies do not transition to 4hrly E at 4 months but more towards 5 or 6 months so I wouldn't be in too much of a hurry to stretch as far as 4 hrs if he doesn't seem ready. BF babies often have a DF and another NF at this age although I don't think I'd expect him to wake every 3hrs.
There's also a GS at 4 months so there's a chance of day and night feeds increasing through the GS.
hth