Hmm. Well, I'll take a shot...For starters, here is a very basic look at fishing in the park at this site:RMNP Fishing
But keep in mind, this is a HUGE park and many of these lakes/spots are not easily accessible. I would suggest getting a good map of RMNP, and cross referencing where you are camping against this list of fishable rivers and lakes. About 2/3 of the lakes in the park have no fish- (too cold? too high? not enough oxygen or food?).
My own suggestion is that a 4wt rod is all you need, and would be fun. In some cases, you might even get away with a 3 wt. The altitude (lack of oxygen, food, and short summers) keep the fish on the "smaller" side (I have caught everything from 6 inch brook trout to 14-15 inch rainbows/cutthroats/browns in RMNP "The Park" as it's called locally). But they are beautiful fish, and awesome to catch in that setting. Here is another article
to read that is pretty spot on.
In the town of Estes Park on your way into RMNP, make a stop at Kirks Fly Shop
, they are helpful and have the flies you want.
Here are a couple pics in The Park...enjoy your time! It's a beautiful place.