Just a thought, how about Rand Paul. He seems to be high energy and knows policy. There is some overlap on the issues and it might grab the interest of some libertarian and millennial voters.
Kentucky is adjacent to Ohio as well and that could help.
I think Gingrich will be Chief of Staff, I think since he knows the Clintons well and his daughter is a spokeperson for Trump, Huckabee is on Trump’s list.