Main advantage of straps on a kitefoil board is in the water start. It puts your feet in a repeatable position (so you don't crash as much) and helps keep the board from floating away/sinking whilst you get ready. If you already ride a strapless surfboard you probably won't need straps. Most ride with only the front foot in the straps anyway until ready to jump so backstraps aren't a necessity.

2 front or 1 front is personal preference. I like 2 front because I like to swap feet and ride heel edge mostly. Its easier to go strap to strap with 2 front straps. You'll probably prefer one front strap if you aren't swapping feet as your foot will be further inboard so you'll be able to ride upwind toe side a little more higher.

Straps are also good for jumps. Possible without if you have the time to practice and prior skills from strapless surfboards but the landings are trickier without straps (you want to land nose first with a foil rather than tail first like on a twin tip).

A toe hook for the front foot might be worth considering also, as a handy compromise between straps and strapless. Handy for the waterstart and feeling correct foot placement but doesn't impede foot movement (or risk trapping a foot in a wipeout.

Agree with other posts, front half hook is great. It assists with water starts, and is then out of the way so you can vary foot position and get foot changes going. Also good cause if you crash no issues with feet/ankles getting caught. Picture below is my home made 85cm ply board.