There is no 'normal' when it comes to families as different things suit different children at different stages of their lives. If you are actively involved in their care now, then you have a strong argument for shared care (50/50), but if you are less active, you may prefer to have every other weekend and a day or two in the alternate week (e.g. after nursery for example). Only you know your situation best - these things are often better sorted out in mediation than in court - but if agreement cannot be reached, then court is an option.
If you had your children for 1-2 nights a week, then on your expressed salary, you would be expected to pay approximately £155 per week. This is the legal minimum calculation provided by the Child Maintenance Service (CMS), you are perfectly entitled to pay more if you wish, as clearly childcare and daily living of children will easily exceed £155 per week, but the CMS will only calculate the bare legal minimum.
In relation to the family finances and a settlement - the court starts with a 50/50 split for a medium to long term marriage, or where there are children involved. They then adjust according to the relevant law, which is s25 of the Matrimonial Causes Act 1973. This includes each parties needs, their earning ability, and the children's needs, amongst other things. If the children are with you on a 50/50 basis, the court will try to see if it is possible for both of you to be housed adequately from the family assets.
Does that assist? If anything is not clear, please do ask.