Check out the Exclusive Expressers thread - there's a few stories there (mine as well) and lots of advice.

I pumped 3 hourly to begin with, then 4hourly, at 6 months I dropped the overnight pump and at 8 months I went to 4 pumps a day and continued dropping pumps until we weaned. I also had a good supply and found that as I was dropping pumps, my supply wasn't really affected until I dropped to 2 pumps a day. So if you can get a good supply established early on that is great.

I was fulltime expressing, so when we went out I would either time it between pumps or take the pump with me. She had virtually all her milk at room temp, EBM keeps at room temp for a few hours so I would give her one lot & then express the next.
I had a double electric pump which was a godsend, and I did have other children but they were all older; so we had football games & dance comps & school stuff, but we could work around that.

Two bits of advice I would give myself if I was facing it again - one, keep trying if you can - it might be hard now, but things can change. And long term it will be much easier to breastfeed than to express. I do wish I had persisted for longer , having said that though I tried for weeks & it was doing my head in, I know what a struggle it can be.
And secondly, don't stress too much about scheduling pumps - I was like a maniac on the clock when it came to pumping but really, I had a good supply, and babies don't breastfeed at set times so if you have to have the odd pump a bit earlier or later sometimes, it's not the end of the world. Especially with 3 under 4, you might find sometimes you have to put it down & come back to it later. As long as you're roughly getting 8 in 24 hours, you should be ok. I wish I'd been a bit mor relaxed about it

Goodluck