Well, you've got the ambition going for you so that's good.....
CARB requirements for truck an TRU (trailer refrigeratation unit) its called are a bother. Since I live in the Midwest, I can find enough work to keep me busy without Cali. Think 2008 or newer truck and 2009 or newer reefer.
13 speed is a 9 speed with an overdrive splitter on the high range. 18speed is split hi and lo.
10 speeds are generally specd for mileage fleet trucks. Fewer people today seem to understand how to drive the 13 or 18.
The Detroit's historically have had the lowest maintenance costs over a cat or Cummins. Its reliable and solid. My series 60 will tie hills with most cats and give them a good run for their money.
As to running for brokers, I have some that I work with more often than others, but the key is communication. Say what you'll do and do it. And if you run into a glitch, own up to the fault. Be honest about what you can and will do. It's all you have out here to separate you from anyone else.
You can get business sense from anyplace. SBA, score, etc. Take a business management course too. Basic accounting wouldn't hurt either. That's why I am not a fan of Rutherford or Ramsey. They don't teach anything that's not available even in a business management for dummies book and its a whole lot cheaper.