Moonlighting as a consultant

I have some specialized expertise in a niche engineering market. I have a fulltime job but am thinking about moonlighting as a consultant in the US. Questions about the business aspect below. Right now I am thinking about offering a particular service, running a small piece of software to allow businesses to meet state regulatory requirements. I may also be willing to do larger or more complex projects in the broad area of engineering-niche as well.

I was imaging setting up (engineering-niche related term) Consulting. I have a similarly named domain already. I have no real sense as to whether this will bring in money, or how much.

I could slap up a web page offering these services over the weekend. What do I need to do, or should I be doing on the business front?

Should I set up an LLC or register a DBA? Would starting out operating just as myself and directing clients to write checks out to me personally be a terrible idea? Would not talking to a lawyer/CPA before doing anything else be stunningly foolish?

extra credit: I might like to split up some of the (theoretical) work with a friend from graduate school. Should that be included from the getgo?

Anything you can do to fill the gaping void that is my knowledge of running a business is welcome.