The merinos they have these days can be light and thin and wonderful to wear... Icebreaker, SmartWool, Patagonia and similar have all different weights of fabric. I wish I could afford them.

I get polypro on sale at Sierra Trading Post in different weights. I carry one set of midweights for three season use and a midweight shirt plus a set of expedition weight for colder. I have a lightweight base layer shirt for hiking in colder weather, otherwise use those synthetic REI OxyT shirts during the day - I like the long sleeved version, keeps sun and bugs off. They breathe very well.

Polypro feels fine and works well, but needs washing with vinegar to handle lingering stench. Wool doesn't stench up as bad.

I hiked in rain and then slept in it - my setup on that trip included the hammock and tarp, down quilt, pad, and poncho. Sometimes you just get wet. When I got to camp I set up the tarp and put down a large trash bag on the ground, then got out everything else - I was the driest person there, the tent folk struggled with rainwear dripping all over the interior of their tents, and the poncho tarp user had to bring a jacket to use around camp... It rained all night until early morning. Since I had dry base layer to sleep in, I was fine, and my clothes dried somewhat overnight (I wrung them out good and put them in alongside me) and finished the process while I was hiking the next day. Pretty much how I handle hiking in the rain. If I were still a tenter I would have taken a light tarp in addition if rain were likely, to have a shelter while setting up - about the only way to ensure staying dry. And then the tent could be moved aside, and the tarp could be the kitchen area.