I am the guy you want to talk too. I started mowing at 13 and make a damn good living still doing it. I run this stuff everyday, so I know what I am talking about.
Do yourself a favor and start small but think big. I started out with a 21" and now 7 seasons later got a lot of stuff (list below isn't even 1/2 of my toys, those are just the big stuff used every day)
I would go find yourself a nice used 48" or 52" hydro walk behind for $3000 to $3500. Get a sulky to ride on behind it. It can either have a fixed or floating deck. Floating decks allows for instant height changes.
Used the walkbehind to make some money towards your truck. Then buy trailer and then a ZTR. You can put a walkbehind in the bed of the truck, not a ZTR. Don't make the same mistake I did and get the ZTR first, then play catch up with the rest of the equipment to haul it. Biggest mistake people make cutting grass is buying the neatest coolest machines. Not what they need for the job or what they can afford. You don't want to start off in debt.
I am going to catch heck for this. But JD is not the way to go. eXmark, wright, hustler, ferris, bobcat, scag, encore are much better choices in that order.
I run mostly wright equipment. They can take an unbelievable amount of punishment. I bought my first stander when I was 15. I bought a 48" bunton bullet for my first machine when I as 13.
