You are in a position that men usually find themselves in. There is a huge double standard on display in this thread - if the roles were reversed, I am sure that the comments would be very different about the non-working parent.
However, the everyday sexism of mumsnet is a distraction here, because you need advice! Here's a perspective from a male breadwinner who went through divorce and secured 50/50.
First, remember that the courts are only interested in what is best for your children. They do understand that having a quality relationship with both parents is best, and so they will always try to support that. Your job in this is to make it easy for the judge to see that 50/50 is right. To do that, it has to genuinely work for your kids.
So, start by building a parenting plan. Physically write down how you would make 50/50 work for your kids. Can you adjust your working pattern to ensure you are around when they need you? Can you work at home sometimes? If your having the kids 50/50 would mean they spend lots of time in childcare, rather than with either parent, that probably isn't best for them. So you need to write down a plan, and you need to be honest with yourself about whether you can deliver it. For me, it meant getting a transfer out of London to work locally, negotiating regular working from home with my employer, and putting a high flying career on hold for the next few years at least. They're not easy decisions, but you have to be sure that you can be the parent your kids need.
Consider other factors that influence what is best for your kids. Who do they have the strongest relationships with? Who can best meet their emotional, physical, financial, and educational needs? In my case, there was domestic abuse from their mother during the marriage, so naturally allowing her unfettered control and influence over their lives wasn't going to be a good idea. Think hard about factors that will influence your kids' quality of life. And where those weigh against what you'd ideally want, be honest with yourself about this. Remember - their needs come first, and if it isn't right for them to have as much time with you, face up to that.
Accept that you're going to be screwed over financially. Sorry - that's just the way it is. Welcome to our side of divorce 🙂. Make an appropriate offer, but don't just roll over and hand everything across. Get quality legal advice. A court will usually expect the non-working parent to find a job and support themselves, so don't just assume that because he doesn't work now he won't be expected to in the future. I got taken to the cleaners - it's just the way it is. The court assumes that if you earned the money, you can always make more. So they give it to the other party. You might be tempted to get bitter about that - it's pointless. Accept that this is the way the world works. Personally, I'd always go for the clean break if you can, because I would imagine that paying spousal support for someone who couldn't be arsed to work (my ex was similar) could start to wear a bit thin a few years down the line!
Talk to your kids, and find out what they want. Do NOT lead them! You need to genuinely listen, and be willing to adapt your position if what they are saying is not consistent with what you want.
Throughout all of it, with every action you take, always pause and ask yourselves who you are doing it for. If you are genuinely doing something because it is in their best interests, then you won't go far wrong. It absolutely is possible to be the breadwinner AND to secure 50/50. I firmly believe that this is usually what's best for the kids - but only if you can commit to genuinely being there for them.