Not bad for a first considering all the doodles we've been getting lately. I think the writing takes the eye away from the picture but you have more than enough room to go back and move it, and maybe consider a body.

If by layer opacity you mean fading one layer in and out then in the layer section (left of the screen) where it says layer 1, 2, 3, highlight the layer by clicking on it and move the slider underneath (each layer has it's own) left, the more you move it the less the picture shows. If you mean color opacity then under the tool box it has sliders for opacity and flow. The more you move the slider right the stronger the color, the more left the less. Blend is one of the best options in Lascaux (pronounced las-cow, named after the cave paintings in Lascaux France. I know, useless information but just thought you'd like to know) :)

You have to download JTablet to use the pressure sensitivity. Here it is. Install it and follow the directions and when it's done click on the two buttons on the right of opacity and flow. Then have at it.

They aren't halftones per se, but there are two sliders on the left under paper mask with the initials i and d. These are Intensity and Density. Sliding the bar left makes something close to halftones, with a little experimenting you can come up with some amazing stuff.

The best thing to do Phree is to read 2draw's wiki. It has a tutorial for everything and should help you out.

Hope some of that helps. Welcome to 2draw.