I am thinking about using XenForo for a forum, however the forum I imagine has many customisations and non-standard things in it. I would like to use XenForo as a "base", and develop a bunch of addons for the features I have in mind. Many of these features are specific to the area that the forum will cover.
My question is, how extensible is the addon system? How far can I go with addon development in terms of utilising existing site functions or overriding them completely? For example, if I would like to create a system to allow users to choose from a selection of avatars to apply to their account, but to have different avatars for different user groups, is that possible? Or if I would like to change the login method to add [insert custom login service here]? Or, if I want people to be shown a page before their post is added with perhaps a question/verification or something on it (just an example), how easy/hard is that?
Hopefully people get the idea I'm trying to ask, if not I can be more specific if needed.
I was trying to find an official addon documentation but was not able to find it.
Thanks in advance