I would start with the delrin, that stuff mills so easily. Aluminum last, you need some practice first. I have some bits but I can’t recommend them until I try them.
I have a 1 and 2 flute bits, but from what I am learning I think we should be using single flute as much as possible. Because we use a relatively high speed spindle and a relatively slow machine (because of rigidity). So my videos have all the details of how and what I used but I think we can do better. I have some things to mill coming up soon I will try and run a few tests then and put up my findings.
Up flutes for most materials, square end mills are most common. Wood bits have a inverted point. Plastic and thin sheet material and laminates other than aluminum should use down flutes to minimize splintering and material lift. Ball nose are usually for finishing passes or pretty pocket cuts.
Just the .02 tour.