I don't live in the UK, but in a country where 50/50 or near enough is the norm and now few people have sole care. Here there is a simple formula for working out maintenance and you might find it a useful one to propose to your husband, as you are proposing 50/50.
Work out the costs of housing/food/clothing/after school activities for each child and do the same for each parent. For housing for example 1200 = costs of the house / 4 occupants = housing cost per person.300 per month. Agree upon these costs. Let's say for example the total costs for the children, in both houses, all added together is 2400 per month.
Now add your salaries together. 12+32 = 44k. Now do each salary as a ratio. 12/44 = 27%. 32/44 = 73%.
Now take the 27% of 2400 = £648. Now take 73% of 2400 = 1752. Now take 50% of 2400 = 1200 as you need this to work out the equality in this maintenance. Now 1200 - 648 = 552. So £552 is what maintenance your husband would be obliged to pay YOU as you earn less, but that would make you both pay exactly the same proportion of your incomes to bring up the children.
Then you consider how much child benefit / child tax credits ONE parent receives, as it can only be one parent. It makes sense that the lower earner receives these extra children's benefits. For example, your children's benefits add up to £400 per month. 553 - 400 = £152 per month. That is what in the end you receive in maintenance. An alternative to reducing the maintenance with these children's benefits is for the parent in receipt of them to buy all clothes, pay for all after school activities, this will work if the total of these costs is equal to the children's benefits, in which case you remove these costs from the initial agreement on the "costs for the children".
If your income increases, or his income decreases, you re-calculate. You could do the maths once a year and set the maintenance for the following year.
This really is the fairest system. It means each parent pays not exactly the same but pays the same proportion of their income on the children.