There are lots of unknowns the first (and likely only) time you do a dissertation. Things can seem foggy, vague, overwhelming, etc. One of the things you will that can feel (and be) very high-stakes is choosing your dissertation committee. The following article provides some really good advice: https://www.insidehighered.com/blogs/gradhacker/choosing-committee
One of the things I particularly like about the article is the way they characterize choosing committee members as INTERVIEWING them. This makes sense. These are the people you are going to rely on as move through the rollercoaster of writing your dissertation. I strongly encourage you to consult with your chair first, but then explore the partnerships that might foster your growth and success. These can also be relationships that lead to further collaboration after you successfully defend your dissertation.
Do your homework and talk with your peers about their experiences. Figure out what you need (and just as importantly what you do NOT need) and then invite the faculty you would like to work with. Remember that they might say "No." That response is likely not personal. Rather, strong faculty members whom students enjoy working and learning with can often be in high demand. They have other obligations and may only be able to manage so many students at a time.
Best of luck as you draft your team. Hopefully, after the first conversation or two, the fog will begin to lift and things won't look quite as scary as they might at first.