#1 No difference really take you pick.!
#2 Any spare output you want to use. Then set Mach3 Enable output to that pin number.
#3 Use the Fault Input.
#4 Because when you trip a limit then you need to temp override that limit to drive off the switch.
#5 Yes
#6 Google is your friend try this.! http://www.is-com.ru/files/PNOZ_X9_en.pdf
#7 Can only use three phase if it's a Three phase Input which it won't be unless you asked for 3 phase input VFD. If single phase Just use R & S or R & T both work.
#8 This so you can see it's powered up on the outside of the control box. Personal choice but I prefer to see if box is powered so it doesn't get left on.