Definitely use Tinkercad or (even better) Onshape (or something similar) instead of Bambu (or Orca or Prusa) since Bambu (et al) are NOT cad programs and are NOT in any way precise with holes, countersinks, etc. - it's what the program is designed for. It's a slicer. It can do some additional things as conveniences, but they're not precise. Use a CAD program, even a simple one like Tinkercad (which I really like and use a TON), for anything precise.

Good progress!