Ok I have to admit, I did not read your wall of text past the first question.
Here are some issues with the MFM than FMF thing.
Getting an MFM is about as hard as getting a mosquito bite in a swamp for most couples.
In an FMF the extra F is called a unicorn for a reason.
So don't expect an FMF anytime soon after.
We started with a couple and I think that worked out the best for us. As newbies we were very turned on by the idea but still had the usual jealousies and nervousness. By each swinging with a new partner we were 'even' and as a somewhat possessive male I felt 'even' with the other man as well. I did have a bit of jealousy after our first time but I justified it to myself by knowing I had sex with his wife too. These days its not an issue, but sometimes you don't know you have demons to slay until you face them head on.
Another thing we have seen over the years on this board are people who first do an FMF or MFM and then their partner decides they don't want to do more, or are uncomfortable with the opposite. Its the whole fairness in swinging concept. Starting with a couple means we had our cake and ate it too, there was nothing to be resentful of.
So for some I'm sure your plan is fine, for us, couples were the way to go.