does entopy affect equlibrium in the sense that you are continously redefining your equilibrium due to the universe leading to increase in entropy. (2nd law of thermodynamics)
Yes, entropy can affect an equilibrium - though I'm not sure how important this is for the mcat. Generally, if a reaction produces 2 products from 1 reactant, the product side of that equilibrium will be favored (i.e. increase in entropy is favored).
In organic chemistry you often talk about entropy being a "driving force" for some reactions.
I'm not sure how you rank entropy as a factor in terms of its effect on equilibrium but it is a good question. I think I've only considered it during Lechatalier type questions (especially for pressure and temp) and obviously when calculating delta S or delta G. Hopefully the question itself tips you off that you need to look at entropy. Most of the time though, in kinetics and acid base reactions, I just look at Keq and and let the concentrations of the products guide me and of course heat changes when present.