all the rivers you mentioned can be/are very productive and are within a 1/2 hour to hour drive from kelso. the south fork toutle is a beautiful river to fish and the view of mt. st. helens always seems to amaze me on the way up.
the kalama has plenty of walk in access and lots of places to find holding fish. the lower hatchery has a nice run below it and a deep pool on the far bank with a few big boulders strewn into the mix. the top of the kalama at the 1000' foot mark (there is a nice downhill stroll,) almost vertical and a really nice glide with lots of holding areas after the leisurely stroll down the cliff!
the cowlitz, i have not fished yet and would like and if i were not moving to the east coast i would defeintely hit the cowlitz and other rivers with you. a lady i was speaking to the sportsman's warehous mentioned that there some steel being caught.
other rivers to consider would be the washougal, the sandy in oregon, wynoochee, satsop and a plethora (damn blazing saddles heightened my vocabulary!) of others within 1 to 1 1/2 hours drive.
if you can get hold of a non mototized boat (drift) of a float tube there is also merrill lake that has outstanding cutthroat and rainbows.
too many places to fish, not enough time!!!!
as far as a license, hit any Big 5 (sporting good store), or the (for the life of me i can not remember the fly/bait shop on kalama river road) along the main road on the river. you can buy them online also, i believe.
if i can think of anything else, i will PM you.