Gaiters can be great for walking through grass / shrubs / trees when they're wet. They help protect the lower 3rd of your rain pants.
Proper types of fleece layers continue to insulate well even when wet, unlike cotton. Cotton is basically always a no-no. Wear merino, synthetics (polyester), spandex, fleece, and when you're dry and not moving much, down fill.
I wear a pair of
Salomon 4Ds for winter use, they're decently warm so you won't need thick socks if it's cool out or your boots get wet. They're GoreTex (look for this in any shoes you buy) so they breathe okay but don't let water in. Always put your pants + gaiters OVER your boots so water beads down onto the waterproof outer of the boots.
You'll need rubber boots if you're gonna be in water any higher than a few inches (factor in splashing) but for grip, warmth and comfort, gum boots suck.
Take dry spares of socks and under layers depending, a dry bag could be handy (dry backpacks are likely common on the West coast).
.. That's all I can think of for now.