Hi Sarah and welcome to the BW!
I think you might need to look at stretching your A times to 2 hrs so that some of those naps are consolidated into 3 naps (2 x 1.5hrs and 1 catnap) as I think he may be having too many sleeps during the day, which is probably also affecting his night sleeps as his bedtime is quiet late. We usually work on a 12 hr day
I would try and aim for something like this:
7am - wake and feed
9-10.30 - sleep
10.30 - awake and feed
12.30-2 - sleep
2 - awake and feed
4-4.45 - sleep (catnap, so just a short sleep is needed here)
5pm - feed
6pm - bath and bedtime routine
7pm - bed
Start by adding around 15 mins to his A time every 3-4 days and you might find that he will sleep longer in the cot when you stretch his A time. Try to do the morning and afternoon nap in the cot. Its ok to do the last nap/catnap in the pram because this pram is usually short and will disappear anyway by around 6/7 months. I would use the shh/pat method to settle him past 45mins if he's up earlier from his nap and if you can't settle within say 20 mins or so, then you could give him a little more A time and keep him up until the next nap is due but offer the nap a little earlier (so say around 30 mins earlier). That way you are more of less in line with when he would have his next nap and the whole day is not thrown off. The E's I did 3.5hrs apart as if he is a breastfed baby, he might not be able to stretch the full 4 hrs (my DD, who is also 4 mo can't). But definitely bring bedtime to an earlier hour and 10pm is quiet late in my opinion as most babies do 11-12hrs at night.
Let me know what you think