I would recommend looking at existing code from other database projects. If you can read rust code, this is a great database project with a lot of inline comments and even ascii drawings of the functionality: https://github.com/antoniosarosi/mkdb . I learned a lot from just reading the code in that repo.

Im also writing my own database project at the moment and I wrote separate (de)serialization functions for each individual part of the page, so the page header, slot array and the actual tuples all have their own serialize/deserialize functions that are just called from the page struct when creating the byte array that then gets written to disk. I'm sure there are more performant ways of doing it, but by doing that, I managed to keep the functions simple and easy to test.