You have already learnt how to split your time between children so that will be no different with another one.
Things I would say which I find frustrating are:
A lot of holiday packages/rooms/special offers etc seem to be catered to families of 4. Holidays abroad just seem so expensive now, there doesn’t seem to be as much choice for families of 5, although that may not bother some with plenty of cash to spare.
I can never choose a small or even medium size car. As even just going for a day out feels like I’m leaving for the weekend with all the stuff you need for 3 kids!
Maternity pay, I just accepted that I wouldn’t have as much money to throw around once my work mat pay ran out. I planned and started to ease off the spending before I finished work so had some extra to help tide me over. Financially I was well ready to go back to work but am glad I took a year off each time with my babies.
Nursery fees (dependant upon where you live) eat a big chunk of cash but only last a few years it’s over before you know it and then you feel rich again once they start school.
I felt the jump financially from 2-3 kids feels a lot worse than 1-2.
Only other thing is I never feel like I can just drop in on friends anymore. I’m not sure how to explain this but it feels like we are a big group now but maybe that’s because mine are still young (10,8&6) so I feel like a whirlwind compared to my friends with their peaceful life with 1 or 2 children.
My oldest is a mummies boy and has said a couple of times over the years that he wishes he was an only child so we could go on more adventures and I do agree with him to be honest. My friend with 1 child has mentioned her son has asked for siblings a few times so I don’t think you can win really on that front.
Maybe Iv just stated the obvious but they are the main things I wish I had considered more before having a third. Would they have changed my desire for 3? Who knows!!
Good luck whatever you decide!