We do 3 school runs, because they go to 3 different schools. 1 primary and 2 different secondaries. Combine this with 1 or 2 of them doing an after school club and it can add up to 5 children coming out at 4 different times.
Ex wife got snotty a few years back because he was refusing to let children attend after school clubs because of all the ferrying about. She threatened to stop him seeing them on school days, so now he just fits round whatever they want to do. He really struggles to get them to tell him when they are coming out of school, so sometimes he sits and waits and they don't even come out.
DP is a big earner (which is amazing considering the amount of holiday he takes, how many other fathers have their children for over 6 weeks of the holidays in a year as well as being there if they're sick and before/after school) so if I were to give up work, we could manage, I just don't know if I could stand him picking fault with every penny I would spend on DS. I suspect he would say his kids could have more pocket money, for example, because they go to local school which involves no bus fare, whereas I have to pay for bus fare for DS. I think he likes the idea of me working, but not the practicalities. He doesn't like it when he has to come home and cook his own dinner sometimes or when I don't sit down to be with him til 9pm.
If he says "no" to his ex, the kids won't attend clubs, see their friends etc. This does happen, although eldest 2 get on public transport sometimes now from their Mum's house. He is very keen for DSS to pursue any amount of sports and organises things for him, but because he doesn't like dance / drama, he is putting off organising anything for his daughter. I am stopping myself from organising it for her because then I feel, I am adding more to the already massive agenda.
We do get time as a couple, but not on contact weekends / days. DS goes to his Dad's every other weekend (although this is a bit hit and miss) and DSC are with their Mum. Sometimes DP will go off and ferry kids around, but at least I'm not left with 3 in the house. So, he gets his quality time with me, time with his kids - he's happy. Simple. 
I had a partner before I met DP, who I didn't live with and who tried to insist I had his kids while he went off to play golf. His ex wife backed him up and told him I was being unreasonable as I had had them when he had gone to work before. Basically she didn't want her kids and neither did she, but the kids were told that "redhen doesn't want you". The kids were left to roam the streets and wait outside the golf club. When I see those kids now, I still feel terrible for them. I know I did nothing wrong, and the "real" parents were the ones who should feel ashamed. I just wonder if I am odd and uncaring? I feel pushed into a corner, where I have to look after them and if I don't, then I am obviously some sort of wicked witch.
I do wonder if he really appreciated the effect it has on me and on DS. When we talked about Sat eve, and I said I wanted to go and see my friend but couldn't because we are committed to his social event, he said I could still see my friend and what a good idea, because then she can come to me. Of course this leaves me with 5 kids to put to bed while trying to have a glass or 2 of wine, while DP swans off with his friends. He honestly didn't think for one minute, I woudln't think it was a good idea!
It was literally only weeks ago, that I sat him down, had a big rant, calmed down and calmly explained that I feel this is not my home, I am not respected, I am not happy and I have a very strong urge to go back to my own house. My house was "between tenants" at the time and the draw to go back was very strong. He got upset, kept saying how we have something special and said he would consider my needs a lot more. Since then, he has been "asking" me every time he runs up the road for 20 mins if it's OK with me. God knows what he would do if I said "no". Probably pack all the moaning kids in the car and tell them "redhen doesn't want you". He told me he would definetely consider what I wanted when it came to school holidays as he knows what upset it caused last time. So he snaps at me before he even asks me, makes sure he asks me in front of DSD and tells me how she will be "turning up" whenever she feels like it as she is old enough now. I suppose I am waiting for ex wifes response before I go nuts at him because she might just want to have her kids for more than a few days in the holiday. That's what I'm pinning my hopes on - a woman who won't even meet me, hoping she can make me happier than DP can!