Sounds like a profitable venture. Street sweepers will out-perform manpower (push brooms and/or blowers) at 50 to 1 in speed, cost, etc..., depending on the size lots, streets, etc... you are going to clean.
As for your questions, there is almost no way to answer them in print, because each lot or street is different. As I tell folks who call me for a bid, on the phone, "I have to come take a look at it". Sometimes persons will start telling me "oh it's a 20 ft. wide road that's one mile long. How much for that? If I try to quote them an hourly rate, they'll often say "well how many hours will it take?", to which I bring them back to "I'd have to see it, because obviously, the dirtier it is, the longer it will take". It also depends on their objective: Do they want it so clean that they can lick the surface and nothing sticks to their tongue? (as in, absolutely dust-free, as in for striping or tack-oil purposes), or merely just for looks where a little dust or water smears isn't important? There's simply too many variables. In an hourly rate THEY call the shots and THEY determine how much and how long they want you there.
Often times someone will become agitated and STILL think they can get a phone bid, by saying "well how many square feet can you cover per hour?" To that I'll tell them "I've done 100K sq. ft. in an hour, and other times taken all day for only 10k square ft.". It just depends on how dirty it is, what their objective is, whether or not there's corner and bumper blocks to work around (hand work, blowing, etc...). Even then, some people still don't get it and try to start to describe how dirty it is (like "oh, it's only some rocks and dirt, blah blah"). I will keep insisting there is no way to do a phone bid, because I can't be held to something I haven't actually seen. Once I see it, and go over their options, THEN I can decide how long it would take, and give them an accurate bid.
An exception is sometimes city street municipal work, where contractors have been known to bid by the "curb mile". But even then, they usually satiisfy themselves that the streets are extremely ratty, odd-shaped difficult gutters, etc.....
The only reason I bring all this up, is that it would be nearly impossible to coach someone in printed text, on how to bid, and how to start a business. There has been some booklets published by the San Jose, CA based company MASCO on "how to start a parking lot sweeping business", but I would caution you that it's probably with the american shopping center and legal climate/culture in mind. Ie.: things where you are could be different. It's a start though. Drop them a line and they'd probably send you the booklet for free.
And if you want to pay my air-faire out to the carribeans, I'll give you consulting for free
25 yrs. experience