We used to have a contract similar in scope, it was a boat yard for dry docked boats.
This job will take you significantly longer than you think it will I suspect. The job we did was a little smaller than yours, I sprayed out of the back of a pick up truck with a 50 gallon sprayer. We sprayed 2x per year, soil sterilant was not allowed due to large trees surrounding the property.
It took me almost 8 hours to spray each time, walking between all the boats, moving the truck takes a long time.
I thought you had a decent price until you said it included mowing, I would not touch that job for $700 per visit (based on the numbers you gave $2000/3)
I dont know what your market will bear or your costs but, I got over $2000 per visit and still hated every minute of it.
"What do you mean we canít get rid of those weeds in time? Then go over there and put some fancy signs with Latin names in front of them."