Polypro base, maybe fleece over it. Definitly expidition weight. Or military ECWS weight. (pretty much the same thing)

As far as keeping bulk off the arms, make some of your layers vests/sleeveless. The main thing is keeping your core warm. You'd be surprised how well a good vest as a layerwill do in colder weather. If I'm walking alot or can expect a cold snap, I'll just add a stuffable down vest to my pack to put on under my jacket if it does get cold.

That would help reduce bulk in the arms for you.