thanks for the good questions! I always find good stuff to chew on when I post here.

How many kids would be expected to be older than your 2 year old once school starts?
That's something I'm thinking of having DH call again and ask to see exactly what the age distribution is. Most kids start some sort of school between 2-4 so I am slightly worried that it could favor younger kids. Then again one of schools we're looking at for elementary school wouldn't start preschool until 3+.
Starting over in a second language buys you some time, so that is a good thing. You have a community there - that's good too. Do you have to sign up for the whole year? Is it worth it to try 2 days at one place and 3 days at another?
Can you take a visiting trip before you enroll? It might make a big difference.
That's what I'm hoping for. We would have to sign her up for a semester i.e. 6 months and we'd need to do it now since the spots fill up fairly quickly. So we wouldn't be able to try it out ahead of time.
She actually does understand the language pretty well, though, but she just doesn't speak it nearly to the same extent as English. She used to be about equal with both languages but she's had a language explosion recently and will speak in 5-6 word sentences in English and sometimes just in single words and up to the most 3 word sentences in the other language (but with a more limited vocabulary).
We will visit ahead of time once to set up the apt and other odds and ends but unfortunately it will just be a couple weeks ahead time since we'll already be in the country visiting relatives (different city). The tickets are $1000+ each so we can't afford trips too often.
Some Montessori are terrific for some kids, and others, not so much.
I worry too about that because I know some Montessori schools are very strict on how you can use the materials and I just don't see that flying well with DD who does a lot of pretend play.
One last idea - playdates and your own social life. It's always nice to meet the kids who have local parents to become friends with at your new location. Even though I'm sure you have many friends from 'pre-child' days, it seems helpful to have some friends who have kids who are going through somewhat similar things to what you are going through.
Smiles, and best Wishes,
Grinity
Oh, that's definitely part of the plan! We're trying to move to a neighborhood that does have a number of Americans so in case we don't send her to a bilingual school she can still get English exposure. We actually do know 2 families (both our bilingual families like ours) there already with young children although they live pretty far away from where we plan on moving to.