The Snake River just behind Keystone is up and we are planning to run it late tomorrow (Tuesday). I think it is only considered a Class 4. It is a fairly low volume creeky run (despite being called a river). It is not too crazy in there, but with a couple of rapids we will definitely scout.
Most of my friends progress initially in creek boats by simply paddling runs they are already comfortable with in their small boats. It seems that getting used to the handling of the creek boat is more important than trying to jump into technical creek runs right away.
Maybe one of the most magnificent and beautiful "sort of easy" creek runs in all of Colorado is Castle Creek in Aspen just above Slaughterhouse. Castle Creek is short, but you get to continue down Slaughterhouse right after the creek. Some paddle small boats in Castle Creek, though a creek boat would definitely be more suitable.
But about tomorrow, the Snake River is really not too nasty. I will paddle my small boat there only because I am resisting moving into a creek boat until my little film project is finally shot (I want one boat in all scenes so as not to confuse non-boaters).
Though not too difficult, the Snake River is definitely a run suited for a creek boat.
I guess my last suggestion would be to make sure you paddle creeks with people you can count on to look out for you and who preferably have some rescue training.