Wow - thank you all for the responses.
I guess I had been thinking that there wasn't much point in seeing an accountant (don't know why I said attorney!) yet, until I had the final numbers, thinking that anything they did now would be hypothetical (useful ballparks academically to me but not the IRS), and would need to be redone at the time of filing anyway.
But if there is a way it could help in the meantime, then I'll go ahead and follow up now. And I'll certainly raise the question of state domicile then, as the more I read about it, the less clear-cut my circumstances seem in that regard.
To clarify a little in relation to the replies, I'm employed by a UK (not US) company, and have a 5 year work permit, with what I understand to be the possibility of applying for ILR after that. That may or may not make the social security/medicare tax question easier to answer, but I will take that up with the accountant too and let them give me the good/bad/indifferent news.
The contrast to last year, when I was able to just file a simple 1040EZ in the US, does irk me. Sigh.. I did have to go and complicate my life by living in another country, didn't I?!