I can't answer you question but, some food for thought for you...
Why pay cash when you can usually get 0% financing?
Working on weekends puts you on your customer's lawns while they're trying to enjoy it. I only mow on Saturdays at vacant properties or after checking with the customer to see if I would be disturbing them and I NEVER mow on a Sunday. Furthermore, most customers don't want their lawns mowed on Monday because they want it looking freshly mowed for the weekend. Thursday and Friday are the prime mowing days in my opinion.
As far as mowers go, I feel that a commercial walk-behind mower, preferably a hydro one, is more versatile and the best mower for a start-up that needs something more than a 21 inch mower. You can add a riding platform (sulky/velkie) for larger lawns. The disadvantage is using a grass catcher instead of a vacuum bagger system, but they are available for walk-behinds.
I hate to be negative, but I'm not sure that your business plan is ideal.