Looking at buying a truck

Hi, i'm working for a company as a driver hauling automotive parts here in Michigan, Local & OTR. I started out with my own authority hauling cars with a dually & 3 car wedge, the insurance was killin me and had other financial issues so I went looking for a job, landed the one I have now last November. I am at the point where I am sure I want to stay in the trucking business, cant imagine doing anything else, but I have a strong desire to be my own boss and make better $, company driving is ok but pay wise, I'm not impressed. I have been looking at buying my own truck and working as o/o for the company I'm currently with. I dont want to get too high of a payment so I'm trying to find something for around $15k. I found an 07 Intl 9400 that looks nice/clean, new tires & brakes, autoshift, 845k mi., has a cummins isx 450. Its local and I'm planning on going to look at it this week. I'm kinda scared with those miles, thats my hangup right now with this particular truck. I have an idea of what the other expenses will be, bobtail insurance is way cheaper than what I used to pay hauling under my own MC and having to insure everything ($1000+ month). Any pointers as far as what to look for as far as mileage and that autoshift sounds nice, I'm used to 10 speed manual but I really like the idea of auto. Any input is appreciated. Also found an 09 Pro Star Imaxx with a new engine for $24,900 but idk if I want to spend that much to start out. Decisions, decisions.......