My thoughts:

The following answers are based on an unknown player and are obviously subject to change once you have more information.

1. Opponent's stack size:
Short stack- Assuming that the player knows how to play a short stack correctly, I would put the short stack on a tighter range of hands since they don't have implied odds to play suited connectors and small pp's. I would expect them to try and get it in with TPTK and TPGK type hands on the flop and turn. Many players in the micro stakes do not know how to play a short stack correctly though, and so sometimes I change these assumptions.
Med stack- Wider range than a short stack but tighter range than a full stack because some hands cannot be played profitably without implied odds.
Full stack- A player with a full stack can play suited connector and suited gapper type hands profitably so these are added to the players range. A player who buys in for a full stack is more likely to be a decent player or a reg but I've still seen 75% VPIP from full stacks at 10NL.

2. Opponents opening size:
Without any reads I assume that a limp has a much wider range than a raise. In theory we want to play big pots with our big hands and small pots with our marginal hands, so generally the bigger the raise the tighter the range I assume. Sometimes people will go against theory for deception, (e.g. making a min raise with aces and hoping for a 3-bet) so this is heavily read dependent.

3. Opponents position:
Assuming our opponents are paying attention to position (which may not be the case for some opponents at 10NL where I play) then the closer to the button the wider their range become and the farthur from the button the tighter their range becomes.

4. Re-raising and 3-bet size:
I generally assume the larger the bet the tighter their range is because people usually play big pots with big hands. Again this point is very read dependent. For example, one player may 3-bet small with a strong hand and another player might do it as a bluff.