Don't forget - with doors off VNE (speed) reduces.
e.g. Bell 206:-
With rear doors off down to 87 knots
With front doors off 69 knots.
This will significantly reduce your range if you are going location to location.
Better to use opening window with handheld gear.
If, as you say, substantial overwater flying is involved, you will need either a float equipped aircraft, or if you are away from engine-off distance from land, a twin-enginned helicopter - significant price increase.