Thank you both for your detailed replies, most of which I had not thought of.
My sweater is knit in one piece across the sleeves and yoke, and then stitches are picked up from the edge and knit in the round for the body. Nonetheless, the information you've provided is very helpful (even if I didn't take your advice on all points--mainly because I started it before I asked these questions [yeah, dumb move, I know]).
As for having a discrepancy in the sleeve length, can't you measure the one you're working on against the other worked one by folding the piece in half? They should be symmetrical, and it should be easy enough to line up the underarm sections I would think. At any rate, I'm still working across the neck opening, so I guess I'll figure this out when I get to it.