OK there's a lot to discuss here.
First off there is no legal combination I know of that can tow a 307 (15K lb machine) without a CDL. A 1 ton which would be too small to safely tow 18-20K lbs IMO, will have a GVW of at least 10K. You will need a 18-20K lb gvw to tow the a 15K machine - that puts you in class A CDL territory.
Any combination of truck and trailer that's over 26K pushes it into CDL territory with the exception of a 26K GVW truck pulling a 10K trailer.
I didn't really think about the insurance. How much coverage would you need for that kind of work?
I'm not being snarky but you've got a lot to learn before you launch a business. In order to be legit you'll need at a minimum general liability and a commercial auto policy. Depending on your state laws you may be able to opt out of workers comp. if you are the only employee.
The cost of insurance varies widely from market to market and state to state. I would budget $5K a year for GL and auto for one machine and one truck. GL is based on your payroll - both employee and sub in addition to your annual volume. If your volume increases so does your GL. For example just GL can run $20K or more a year (there are many, many variables that dictate price) for $500K a year worth of work.
One also has to decide what type of corporation you want to set up. LLC's are quick and easy to set up and come with the protection of a corporate vail. Then there are C and S corps as well. I wouldn't suggest going as an individual proprietor as there is little legal protection if something goes sideways.
You'll need a good accountant and a good lawyer. Having a good accountant is crucial in running a successful small business and if your in the business long enough you'll need a good lawyer..:cool2
Owning a small business is all about managing your risks. Risks come in all shapes, sizes and forms and you need to protect your business and yourself the best way you can. Of course you don't have to be a corp. or have insurance to go out and work for individuals but one lawsuit can take away everything you've worked for up to that point. Furthermore you don't have to do anything wrong to be sued, there are opportunist out there that are always looking for something for free.