So I have made contact via email with a law firm in our area that does offer mediation for no fault divorces, which is the way we plan (hope?) to go. I have to call them to make sure there is no conflict of interest regarding them working with us, and then we can set up an initial consultation. The initial one-hour consultation is $100, and then he said that the hourly rate is $175-240, depending on which attorney does everything for us. I like that it's not a huge retainer and that we will just pay the hourly rate. I have heard positive things about this firm, and I really expect (unless my H morphs into a total d-bag, which I am FULLY AWARE could happen, although I am hoping not) that it should not take a ton of time to hammer out the details, provided we were both being truthful about how we want to split things.
I also called my therapist's office today got an appointment to see her on Wednesday. My previously scheduled appointment was not until next Tuesday, so I am glad that I was able to get a spot to see her this week so I can debrief. My next big step is to tell my family, which I have not yet done. I am going to wait until after I see my therapist and probably do it within a couple of days of my next appointment with her, again for debriefing purposes.
Starting tomorrow, I am going to start going through the house and dividing my stuff up into "keep," "toss," and "donate" (I feel like an episode of Clean Sweep). which is going to take a ton of time. I have a LOT of stuff. I don't want to transition everything to my new apartment when I eventually move, so I am going to take this opportunity to downsize considerably. I think I will do a room-by-room effort at first, and then eventually I will have to go through our bedroom, which will be an enormous time suck. I am going to start moving stuff that I don't necessarily use on a day-to-day basis into the basement, which will be my "staging area."
I am right back to that sort of numb feeling I had when I first found out about my H's affair, for the most part. However, I have been indulging in crying jags every morning on my way to work. Half of my commute is on one highway, and then the second half is a different highway, so I have been "letting" myself have a good cry until I reach that second highway, at which point I pull myself together so that I don't end up showing up to work looking like a hot mess. It's amazing how letting it out in the morning makes it easier for me to hold it together all day.
Anyway, thanks to anyone still reading! I am relieved to be taking these first steps, although I am totally aware that the roller coaster is still in the very beginning stages.

Re: Calling an attorney this week (among other things)... (long)
They see us rollin'...they be hatin'.
This part will fade, I promise. Its horrible, but it goes away.
Just an idea- if you and STBX are actually working it out in regards to a settlement, consider using a paralegal group. It's what we did, you fill out a questionnaire, and then they do a divorce decree and then you file it with the state. Ours was a total of $150 including a child custody schedule.
BUT I knew my Ex's finances in and out. He had no way to hide anything from me. Well, in that aspect anyway.