You'll need to stay very busy to make it worth your effort to haul that 4300# monster around.
Rates? Is the tractor paid for? Are you retired? All those types of questions come into play. If you stay busy you'll have higher equipment maintenance costs so you have to be paid enough to cover your expenses and put money in your pocket too.
As rico304 stated, the insurance aspect is often neglected by entrepreneurs just starting out. You need to check your local codes to determine if licensure is required (this stuff gets ridiculous), get good liability insurance (you can never have enough) and contact a lawyer. Any time you do work for other people, it's not a matter of if you'll be sued - it's when.
The ones I know around here, wouldn't get less than about $35 per hour for brush cutting. Finish mowing would be another story due to slower mowing speeds.
It will also depend on local competition and how much your customers are willing to pay you for something they can't or won't do for themselves. I'd start at $40 per hour, float the trial balloon and see where it leads. Your start-up expenses have to be pretty high for the 5105, MX6, a minimum 7500# trailer with brakes and a 3/4 ton diesel pickup plus your insurance. I can't imagine trying to start a commercial enterprise with anything less. Keep good records for the tax man!
All things considered, anyone with a much smaller tractor, trailer and truck will cut your throat. They could probably do the same work much cheaper. However, there's a trade off here for how quickly you can do the job with your tractor. You should definitely be able to cut 4+ acre tracts faster than someone with a 2320.
Disclaimer: I do not operate my tractor commercially, but I did stay at a........... Sorry, wrong disclaimer. Common sense business evaluations are needed before considering any type of work. My opinions are not worth much just intended to get some more info from you and provoke other thoughts.
