The size_t error goes away if you keep dryos.h and module.h at the top, as in the tutorial.
To find what header you need for some particular function, you could do something like:
grep -nr bmp_on src/*.h
If you really want to declare something twice, you should declare it in the same way in both places. This trick is useful if you want to use a function that's not available on all models (WEAK_FUNC), but it's not the case here, so you should delete the "extern void bmp_on" and just use the definition from bmp.h (which you have already included).
Are you trying to do some sort of AFMA calibration on all the focus points?
PROP_AFPOINT will change the active AF point used with phase detection. If you want to cross-check it with contrast-detect AF, try move_lv_afframe and get_afframe_pos. You'll probably also want to change PROP_LVAF_MODE to switch between the two methods.