How can I determine what a medical retirement would look like financially, and how do I go about the process?

http://www.vetadvocates.org

I'm total perm disabled...when we started my whole thing, we had a vet group do it, they really tried, my thing was just way too involved for them...we found about this group, NOVA, they have a search engine to see who's near you, they also have an office you can also call directly...our NOVA guy did 3 yrs active, plus had done VA-disability law for 35-40 yrs, he also got pro-bono help from a large law firm he did stuff with, as my stuff needed the extra brainpower to deal with it...trust me, and call them, or look up who they have near you...all of theirs are well qualified, they also have vet groups involved, you can also try law school vet law clinics, though those don't always take all possible cases, depending on what the law-school faculty want the law students doing the cases under them to handle, what the faculty think the students are able to cope with, in terms of time and/or complexity...pay whatever consult fee is needed, they may not all deal with med retirement stuff, however, they're all well hooked into a good deal of mil/vet disability stuff that often overlaps, trust me, and call them, or use their search engine, OK? I've sent them in many times on here, as have others, I assure you, whatever consult money they need at first, and whatever VA would allow them of whatever back money they'd eventually get you, would be well spent, promise, they're part of the reason my wife and I, esp. I, found out there's a very definite reason God invented attorneys, promise, don't try to handle stuff like this yourself, stuff like this is serious pro law stuff, it's most definitely not pro se amateur night, I assure you, if you'd wanna chat, trust me, just ask, I'm here, whenever you'd wanna yak, I've been through a pretty fair fraction of what you described, so, even though I never deployed (I tried, I wasn't used), I can most definitely relate, honest, OK?

You may want to consider applying for individual unemployability with the VA, if:
You have at least 1 service-connected disability rated at 60% or more disabling, or 2 or more service-connected disabilities—with at least 1 rated at 40% or more disabling and a combined rating of 70% or more—and
You can’t hold down a steady job that supports you financially (known as substantially gainful employment) because of your service-connected disability. Odd jobs (marginal employment), don’t count.
I suggest starting with a Veterans Service Organization (VFW, DAV, etc) before a company that charges.
According to your post, it appears you only have a year remaining to reach 20. You should verify that all of your years are good years, and verify exactly how much longer you have to reach 20. I understand the check doesn't start until 60 for a Reserve retirement, and that you should have some protection of you have 19 good years. However, it doesn't hurt to be safe, and lock in the retirement before you raise/begin the PEB/MEB process.

Also, my whole thing took six and half years from start to finish, so trust me, I got a really good worm's-eye look at how the whole VA-disability thing actually works, from the user end...I never did the mil retirement and/or MEB/PEB stuff, though I've obv read some stuff on it....