Worrisome
It's great that you are getting this sorted. I would worry less about frequency of expressing and more about making sure you really try to empty the breast whenever you do express;
"Empty the breast" is a misleading expression, though really, as breastmilk is not just stored in the breast, ready to be taken and when it's gone it's gone. That's an old wives' tale and leads to people / health visitors / MILs / idiots coming to the conclusion that some mothers "do not have enough milk". They think of the breast as entirely analagous to a bottle of milk, but it's not really like that.
The breast does contain milk, but it also produces more milk throughout the feed, on demand. That's why, the more you feed, the more milk you produce. The amount of milk is not finite.
However, all that said, you should try to get as much out as possible in one feed / expressing and then there's no surplus itching to get out and getting blocked up.
HTH.
And by the way, it is completely normal for teeny little ones like your little chap to want to be close to their mums for rather, ahem, extended periods of time. It's normal. 4 hours feels like a lot, of course, so make sure you have what you need to make it bearable:
- comfortable spot of the sofa
- good book / magazine
- dvd loaded into the dvd player
- laptop with MN at the ready
- snacks
- cup of tea / drink of your choice
- emery board
- mobile phone
When my DD1 was this age, I watched the whole of House Season 1 and 2 on DVD. It came as a huge shock when I had DD and couldn't lie around on the sofa for days and weeks embrace breastfeeding in the same way. if this is your number one, put your dressing gown and slippers on, get your baby and enjoy some down time important bonding time to establish breastfeeding. I envy you!