COS airspace is a no-brainer. Just listen, write everything down, and if you are in doubt, just ask the controllers. It isn't like you are flying into New York or Miami. They are generally not very busy (peak times can be a bit busy) and are super helpful.
The airfield is a bit of a maze to taxi in, so review the diagram, write down the taxi instructions, and if you are in doubt, just ask the ground controller. You will see everything from heavies to military to light civil at that airfield.
About contacting clearance above: If you are IFR, just state "IFR to _____ (wherever your destination is on your filed flight plan". VFR is when you want to give them an altitude and direction (ie VFR to the west at 12,000).
Have fun, it is a great city and the scenery there is beautiful.