Your second question was talked about some at BlizzCon. (Look at the Restoring History: Creating WOW Classic video in https://us.forums.blizzard.com/en/wow/t/everything-we-definitively-know-about-classic/ around the 41:30 point - close to the end.)
Basically, they do plan to allow addons. However, functions that may have been available in vanilla that could be used for automation of play won’t be included. Additionally, modern addons that could work against the goal of building social community in WOW Classic are ones they may be suspicious of and deliberately break.
So addons automatically figuring out who needs a curse removed won’t work that way, and addons like oQueue that mimic the Group Finder they’ve already decided will not be part of WOW Classic may be intentionally broken.