Q 1: Better for cycle life. OTH, some people do need all the capacity, just remember that it's going to cost you.
"Maybe preserve charging cycles" - nope, you won't preserve anything when running almost full cycle. You will get less cycle life. Cycle Life in specs means the number of FULL cycles. 10 cycles, each one 20-80, equals to 6 full cycles. 10 cycles, each 100%, equals to 10 full cycles.
Total number of FULL cycles, i.e. total mileage - will be HIGHER if you run 20-80, because battery heats less and God knows for what other reasons. Nobody understands this chemistry completely.
"Time to charge" is hardly an issue with 20-80, as this takes less time than charging 5%-100%. "Effort" I don't understand. Every evening or after every trip plug it in and put it on timer. If you are riding so much that battery is empty before you get home - then you need a bigger battery or a gas scooter.
Q 2: Yes, and not "seemingly". Adverse effects of full charging have been proven, as well as discharging below 20%. Especially if it's sitting full charged for weeks.
Q 3: Hard to tell what's better for you. Don't worry if you don't feel like, treat it as disposable. Statistically, running 5%-100% will shorten its life, so you will buy a new battery sooner. Though they die sometimes for no reason, with all the precautions taken.