Welcome to RCU.

First, it would be good to find a local club. Boulder is a good sized city, there must be a few in the area. The AMA club locator: http://www.modelaircraft.org/clubsearch.aspx shows one called the Boulder Aeromodeling Society and their web site is http://www.milehighwings.com/club/index.htm (note this link is slightly different from what's on the AMA club page).

The only planes that can safely be flown at most parks are the smaller electrics, hence the name park flyer. Even those could hurt someone if they get out of control. Flying at a club field is significantly safer. Another reason I like flying at a club field is that they are usually a friendly group of people.

The club can be a great source of information on buying a plane, choosing the components, and answering questions while you're putting everything together. RCU is also a great source, but there is something to be said for being able to pickup the phone and call a friend, or even better yet, putting the plane in the car and taking it to their house to help you through something you don't understand.

If you are thinking of progressing to a larger, faster nitro powered plane, a trainer would be the best choice to start with. There is a list of good first and second planes pinned to the top of this forum. From this list you can choose a size and price range that you like. You said you want to start with an RTF because you don't have the knowledge to choose everything. This is an ok path, but if you are the type who likes to learn, an ARF is another choice. Choosing an engine and radio is not that difficult and there are plenty of us here who can give you information on what works. This can supplement the information you get from your local club and hobby shop(s).

In addition to allowing you to begin learning about component choices, beginning with an ARF helps you learn how to assemble a plane. The instruction manuals that come with the typical trainer will step you through every aspect of assembly and prepping the plane for flight. By assembling an ARF for your trainer, you build core skills that will help when you go to assemble subsequent planes.

Whichever path you choose, good luck and keep the questions coming, people are here to help.