England & Wales child maintenance: is it separate from arrangements for seeing the children?

Yes. GOV.UK says child maintenance and child arrangements are separate. Parents can agree maintenance privately or use the Child Maintenance Service, while decisions about where a child lives or time with each parent are handled separately. Official source: GOV.UK Child Maintenance Service and child arrangements guidance. Guide: https://getinstantlaw.com/family-separation-divorce/what-to-do-first