One of the things to consider when buying a mower for commercial use is the size of the mower. Can you get a 60" mower thru homeowner gates (most are 4 to 5 foot max). I would stick with a max size of 54" and maybe even look at 48" or smaller.
I don't think you will be mowing a lot of super large lawns because most folks who have acreage lawns will own their own mower. For average city lawns a smaller deck that will fit thru a 4 foot gate will mow fine and not take a lot longer than a 60" when you consider that most of your time will be in unloading, loading and tiedown.
The Ferris IS700Z with the Kawasaki engine and 54" deck would be plenty for an initial investment in lawn care. You may even have to cut the deck size back to less than 48" size in order to get it thru some of the homeowner narrow gates. Check out potential customers for the minimum clearances you will encounter.
I have had mine for 4 seasons now and mow 6 acres every 5 days of so and then occasionally mow my 6 acre pasture. I had to replace one idler pulley that the bearing started to squall a bit and of course mower deck belts. I put about 100 hours per year on it, change oil/filters once a year in the engine and about every 2 years on the Hydro-gear drives.
You will need to raise the mower up to change the blades, I don't think you can raise the deck high enough to reach under to change. I cant remember the brand, but there is one that raises the deck up to 90 degree angle for servicing. This would be a real plus if you don't have a way to raise the mower up (I use my FEL to raise mine).
