Slowing down and speeding - use the 're-time animation' option.

going up and down stairs - the trick is in the graph editor, make sure the interpolation shows a straight line to stop the feet from sliding about.

saving - use the pose libraries or turn it into a walk cycle, start with the right foot.

cosmology - I'm not going that far! and what you learn in 3 and 4 will help you in 5

Final Fantasy - good animation is possible but they used mocap, that'll work in Poser too but yeah, the renderer's not up to much. For the web however, it's perfectly adequate.

Hair - check out Kozaburo's tutorial and make some morphs, you'll soon be swinging, swaying and bouncing with lifelike hair.

unexpected nudity - the tailor sounds good, personally my site at www.1st-shock.com doesn't need much in the way of clothing ! I tend to go for the options where this isn't going to occur, choose you clothing carefully, but there's always the grouping tool or a carefully placed magnet.

art galleries - I wish there were a forum for showing off animations, there are some relatively inactive lists like Poseamation and Flash_erotica but the sad thing is there just aren't many of us animators here......