Alright. I might update this as the date gets closer, and assuming I don't break down for some reason, I'll let you all know how it goes (as well as the interesting stuff that follows when everything's mostly died down). I hope this ends up helping people.
So, I reckon I should give you some background first. I'm a fabrication engineer at a medium-large sized aerospace company. I work with a pretty diverse group of people, from blue collar to white collar, liberal to conservative, etc. The age ranges quite a bit, say, late teens/early twenties to 70s. Basically we've got people from all walks of life. My job includes interacting and working with all of these groups, since the fabrication department manufactures parts used in every other department. Lucky for me, I get my worth out there by getting my fingers in lots of different pies. I have no problem going to anyone and interacting with them (of course some people are more fun than others), and I do. I actually make an effort to be personable. For as long as I've worked there, I've only received outstanding performance reviews, and have progressively taken on more and more responsibilities... I'm relied on. I'm not trying to flatter myself (not intentionally) but I'm just letting you know that I've put some effort into adding "value" to myself. I'm more of an introvert, and it gets a bit tiring to cater to everyone, especially the difficult folks. I do think this is important, though.
I've had several meetings with management and HR at my work. We've got a tentative date of the day before July 4th before two days of holiday vacation. This might be changed though, so more employees can be informed.
So here are a few of the takeaways from the meetings I've had with management & HR:
1. The approach (as of now) will be to isolate groups based on managerial authority and explain what is going on.
2. A semi-global email will be sent to coworkers who I contact on a regular basis (or may contact). My manager and I will compose this (mostly me though), and probably review it with HR.
3. I will not be present during the day this is discussed. I get some time off

. This is so coworkers/employees can discuss this in private with their managers. I'll likely be taking two days if this isn't done on the holiday.
4. The bathroom situation is still being discussed. They're willing to create a unisex restroom for personal use. I have my reservations because this could be seen as segregation. But this company is important to me, and I'm willing to consider all the options.
5. Open communication was emphasized to me, especially if I experience situations that make me uncomfortable around people. I already know this will happen to some degree, so hopefully I can get my emotional barriers up for this one. I want things to remain professional during the transition at work, but HR wants me to report any occurrence should it happen.
6. We also discussed who already knows at work, including people I've discussed it with and people that found out unintentionally (although they likely don't know the whole story).
So over the next few weeks I'll be writing the letter that's going to be emailed to the company. I'll post it here when it's done. So far I have lots of support. I love my boss; she's really awesome about all of this. I think more than all I'm optimistic, but I definitely know things won't be all easy (especially working in the fabrication department).
*edit*
F-yea! I'm on the last week until my 1 year HRT anniversary! Yaaaay!