Welcome to the forum, turbowarp. You are asking some of the right questions, but probably should have asked them before you started buying equipment. In any case, I will try to answer some of your questions.
Ideally, you work in the business and learn something about what you are doing and how things work. All business is basically the same, however there are some things unique this business which can cause you to lose your shirt.
If you plan on owning and running trucks you have 2 options. You can lease to a carrier or get your own motor carrier authority and do things the way you want, including finding your own freight. The first thing you will need is to have Motor Carrier Authority. If you plan on running only in Texas, you will need to have a Texas MC number. You will only be able to run intrastate with that number. In other words, you will only be able to pick up and deliver within the state of Texas. You may be able to earn a living only taking intrastate loads, but many loads originating in Texas go to Oklahoma and Louisiana. If you cross the state line, you will need Motor Carrier Authority from the Federal Government. Before authority will be given, whether it is for Texas only or interstate, you will need to have insurance. Since your brothers have at least 2 years experience, that should not be a problem for them, providing their MVR's look good. However, if you have not had at least 2 years of recent experience, then it may be more of a challenge for you to find insurance. To qualify for authority, you will need liability and cargo insurance. There are only a handful of insurance companies who will insure a motor carrier.
From your post, I assume that you plan on getting authority. Whether you incorporate or not is a decision you will need to make. If you and your brothers plan on actually being in business together, then incorporating may be the best option. At least you would have some sort of structure to keep things organized. I have owned several corporations and have one for my trucking business. I prefer a corporation rather than operating as a sole proprietorship. You could operate as an LLP or LLC, as well as a corporation. It basically depends on how you want to operate and how you want to structure your business.
You can go out and find your own shippers or use brokers. Most people start out with brokers. Some stay with them. There are a lot of brokers in Texas. You cannot legally broker freight without having broker authority. Broker authority is different than motor carrier authority. The only exemption is for agriculture. If you haul any other freight, you will need authority. You can find your own loads as long as you are a motor carrier and will haul them on your own trucks. Rates have been suppressed in most of Texas for some time now, so you need to be prepared. Since you are a "bean counter" you may want to sit down and look at some hard operating numbers. There are a lot of hidden expenses to operating as a motor carrier. There are a number of compliance issues you will need to adhere to avoid fines. OOIDA is a good resource.
www.ooida.com. Owner Operator Independent Driver Association. They are the primary organization for small carriers, owner operators and drivers. Some of on this forum have had many years operating our own trucks. I and others run our own authority. There are more who lease to carriers. We will be glad to answer any of your questions. You may find some of them by doing a search.