To your first question:
Not that I know off, maybe AweseomeGuildStore is suporting it,check the settings of it.
If not: Just ask the author of the addon you have linked if he can add it to the guild store list too.
To your 2nd question: Sticky post in the forum you are writing. Always take a look at the sticky threads before writing please
https://www.esoui.com/forums/showthread.php?t=9865
->What addons cannot do