Gus has the best answer.
36" is a standard side gate down here.
I have several customers who mow residentials and they all use Greenfields 32" or 34" Fastcut mowers.
You said you were setting up a landscaping business so the extra time mowing should not present a big problem unless you are doing more mowing than landscaping.
As for taking all day, it depends upon how you mow & how hard you want to work.
Dave typically does 20 - 30 yards a day with his Greenfields 34 and that mower has a fixed axel, no diff.
Faster mowing is all about using your head and being proficient with the equipment you have.
I see a lot of lawn contractors with absolutely no idea of how to mow a lawn, working at a pace so slow they are just about standing still.
If you are thinking about landscaping with follow up garden care then make sure you design the gardens to facilitate quick & easy maintenance.
I do mobile repairs and see so many gardens that could not have been more labour intensive to maintain if they were designed by a Government committee.
The same contractors all use anchient HRU21 walk behinds and I am forever replacing worn out 3rd gears and rear wheels.
They fit them with 4 high life blades so the mower packs a lot more grass in the catcher.
A walk from the back yard to the trailer to dump a catcher of grass takes the same time as mowing 1/4 of the yard.
They also us multiple catchers for the same reason in big yards.
After that, a trailer / truck designed for very quick equipment removal will save a massive amount of time.
I have seen 2 contractors working almost side by side and a single man crew had his front edges done , and front lawn nearly finished by the time the 2 man crew opposite had pulled the ride on out, to get to the push mower & edger.
