I suppose my point about the childcare was that if I work mon Tuesday and weds and they are in nursery then they go to him weds thurs fri, I actually only spend one day a week with them
Why would you agree to this arrangement when you go back to work?
You have already told him the arrangement is going to change when you go back to work and as he's refused to tell you when he works, you need to tell him you have changed the arrangement to every other weekend and one night in the week.
As your eldest child is 3 your argument for doing this is that is when your eldest child goes to school they won't need their routine changed as it is in their best interests to have a routine that is stuck to regardless of what else is happening in the child's life.
In your case I would choose the overnight to be day at the end of the week e.g. Thursday when you are not at work so he doesn't turn up you won't have to worry about finding childcare. Yes, that does mean you won't have your children on Friday every week but at least you will have them every other weekend.
In regards to going to Court unless he is threatening to run off with the kids and actually does, then let him drag you to mediation and Court once you have clearly defined your terms if he doesn't agree with them.
If you don't understand why read the posts for posters on this thread www.mumsnet.com/Talk/lone_parents/4000468-Advice-needed-Am-I-acting-wrong-or-illegally
(I know your situation is different but the main points is that you can't force him to turn up and take the children, there as he could use a Court Order or mediated agreement to cause you problems.)
When you see the solicitor concentrate on whether they can help you sort out the finances so you can get divorced. As a PP indicated for child arrangements cases you don't actually need a solicitor you can self-represent.