a good rule of thumb is that you need to go through 50 miles in 10 hours to be on for a sub-24 100 miler. It's possible - I went through halfway on NDW100 in 10:30 and finished in 23:45, but no-one overtook me after 50 miles.
having said that, 24-hour events are easier as you shouldn't get lost, you don't need to carry as much kit etc... At Endure24 I went through 50 in 9:45 and 100 in 21:41 to give you an idea of the difference...
yes, it's possible but you have to get comfortable with pushing through the night sections, minimise your pit stops. On a fairly easy course you could walk 100 miles in 24 hours
Supported means you have a dedicated support team that meets you along the way to supply whatever you need. This generally allows for the fastest, lightest trips, and for an element of camaraderie and safety, since someone knows about where you are at all times.
Self-supported means that you don't carry everything you need from the start, but you don't have dedicated, pre-arranged people helping you. This is commonly done a couple different ways: You might put out stashes of supplies for yourself prior to the trip, or you might just use what's out there, such as stores, begging from other trail users, etc.
Unsupported means you have no external support of any kind. Typically, this means that you must carry all your supplies right from the start, except any water that can be obtained along the way from natural sources. This approach has also been termed "alpine style". The longest trip I'm aware of using this style is Coup's 20-day thru-hike of the Colorado Trail. For most people, carrying enough food for more than a few days to one week will be prohibitive. Unsupported also means unaccompanied!
Depends if you mean an actual "FKT" attempt, like the Pacific Crest Trail, an organised race or just going out for an adventure. I ran the SDW "unsupported" earlier in the year and used taps and a shop en-route but who cares? It was just me vs the SDW...
In the USA there's more focus on FKT's on the big trails - Appalacian / Pacif Crest / Tahoe Rim / John Muir etc... and they have very specific rules about supported vs unsupported. When JB Benna did the Tahoe Rim Trail unsupported he carried all his food but used water as he found it en-route. He did have support but they only met him at certain points and only gave moral support, if I remember correctly he wouldn't even hug his wife in case it was counted as "support"
Taping - I tape my big/little toes, instep and inner heel areas only. those are the areas where I can get rubbing...
Gaiters - I do a lot of running in sand, (on the Wales Coast Path), my shoes have built-in Velcro for DG Gaiters so they were the natural choice. They were a revalation - where I was dumping sand out of my shoes every 5 minutes, I now don't need to take them off and my feet come out clean