Up to you! Established systems will be easier to grab hold of, but new mechanics are always interesting to see and I think people enjoy learning new ways to play. Of course the problem is needing testing afterwards!
Sure! A great source of inspiration for short gamebooks is the Windhammer Competition winners on the Chronicles of Arborell website - this was a competition run from 2008 to 2015 with some distinctive storylines.
https://www.arborell.com/windhammer_prize.html
There is also a fan website for Fighting Fantasy that has original works using the same FF system, though most of these are novel sized.
Hope those help!