I did the PCT in '08. The main suggestion I have is that you get Yogi's guide and read through that ... it does a good job with the sort of questions you're asking. You could also look at an attempt at a PCT FAQ on the postholer site, at http://postholer.com/planning.php.

I used a lot of resupply drops and would use less if doing it again --- a common theme. It depends, however, on why you're doing mail drops. I.e., if you have food allergies or are vegan or something like that, maybe more. It also depends on how much backpacking experience you have; if you've done some long trips, then perhaps you'll be better able to guess how much and what types of food you might want. Bonus points if there's someone at home you can contact to tell them how to adjust type and quantity of food in the boxes.

Finding places to sleep is rarely a problem. I live in western WA state, and it can be a problem there as open space is often covered in brush, so you can be restricted to established camp/bare spots. For most of the PCT, however, it's pretty open, easy to just flop down and sleep.

Ice/snow tools. A light ice axe or an arrest pole like the Black Diamond Whippet is a good idea, assuming you know how to self-arrest, but this very much depends on your particular year and how early or late you go through the Sierras. In 2008 I ended up mailing home both ice axe and mini-crampons, never needed them.

Sturdy pair of boots: I'm in the trail runner (running shoes) camp myself, work fine in snow or whatever. There are people who do it in boots, but even that's kind of squishy --- it's not just black and white "boots or shoes" as there's a whole gamut of greyscale of beefier shoes, shoe-like boots, etc.

Bears: use a bear cannister in the Sierras as required. Basically don't worry about them elsewhere; I personally slept with my food before the Sierras (SoCal has very few bears!), and used an Ursack after the Sierras. If outside of the Sierras you see or hear specific bear sign, then hang your food. Maybe bring an opsak (odor proof) to line your food bag.

Safety from other humans: biggest issue is getting hit on the road while hitch-hiking, or I guess running into someone crazy who picks you up. Biggest human-related dangers will be near roads. For the first 700 miles you'll mostly just see other thru-hikers, and it becomes sort of like a gypsy community of people who will mostly look out for one another. I wouldn't even think about bringing any sort of "weapon". When you say that some have suggested a weapon may be prudent --- have any of these folks hiked any significant portion of the trail in one go? There are risks everywhere; I have a friend who carries a handgun everywhere he goes, but IMO the biggest trail danger is in getting to the trail and back from it on freeways and so on.
Brian Lewis