model them as hovering geometry in the high poly for the AO and normal, and texture just texture them in the low poly.
modeling the the holes, making a contiguous mesh would be overkill imo. It'd be a looping nightmare, esp with the angle of the side being what it is...
If you were to opt of modelling it over sanity, stay away from boolean subtractions, it'll mess everything up with regards to poly flow... start of wish a bridging cylinders with edge loops around each...
something like:
hovering geometry would acheive the same, so as long as, smoothing doesn't conflict:
