Do I need a DOT and MC #?

If you operate for hire in interstate commerce, the answer is generally yes. It is important to note that pre-arranged transportation at an airport, seaport, or other port of entry is considered a continuation of the initial trip. This means that unless all passengers have traveled from within the state, you can be involved in interstate commerce without leaving the state.

The regulations for DOT number, MC number and Financial Responsibility (Insurance), apply to all operators, even those operating only sedans and SUVs, unless they meet an exemption listed in the following sections.
49 U.S.C. 13506(a)
49 CFR Part 372

Here is link that provides a good summary of the regulations.