Hi, welcome to BW and the world of being a mum! Its an exciting and challenging role.
At this age, we would typically see a baby wake in the morning, have a feed and then play for a bit before having a nap, usually 1hr20-30min after he woke. That nap would then typically be about 1.5hr in length and you just then repeat that performance all day until bedtime, so your day might look a little like this:
6:30 - WU, feed
8 - nap
9:30 - WU, feed
11 - nap
12:30 - WU, feed
2 - nap
3:30 - WU, feed
5 - nap
6:30 - WU, feed
8 - asleep in bed for the night
OR
5 - nap
5:45 - WU, feed
7 - in bed asleep for the night
Ideally a baby of this age should have a night that is 11-12hr in length from BT to when they wake for the day.
The length of your little boy's naps suggest to me that he's either overtired, overstimulated or both - this can then lead to the grizzliness in the afternoon. It could also be what's commonly called "witching hour", in which for 1-3hr in the afternoon/evening, baby is unsettled. This can be perfectly normal (whilst irritating and upsetting).
I think the key early on is to get a routine that suits baby, then you can work on him settling himself to sleep once his body is used to sleeping.
Where does he sleep at night? Can he sleep there safely in the day? It might help to have him sleep somewhere he already associates with sleep.