To answer your questions....
Trail...it's not to hard to follow since you will be joined good slug of like minded headlight wearing hikers. The problem comes during the descent when you are whooped and not concentrating. The section between Trailside Meadow and Mirror Lake can cause some geographic ambiguity.
Ice Pick and Clampons...It's May, and even though it is May and the trail may have been forced through cables this year. You should be planning on bringing and using this gear. At the very least you should have will most likely use Microspikes. Never go higher than you can safely descend.
Chains...The passes are open or closed. If they are open, they are clear and you will not need chains.
Half Dome/Whitney...Half Dome is cake compared to Whitney. I do the comparable to Half Dome most weekends during the summer. Whitney 22-miles RT, starting at the elevation Half Dome finishes.
Radios...I hate radios. They are annoying but they do work.
