Thanks a lot for all the answers! 
I’ve just started reading through the ember guides and I realized that all those terms I mentioned earlier are from Ember and not Discourse itself so I’ll find my away around that stuff after I read through the ember docs.
I don’t really think I’m gonna do stuff with the data apart from displaying it but maybe in the future I would.
So then it might be better to just make the API in ruby (even though I’m still new with ruby).
It’d be stupid if I made it in golang or php or something and then remake it later in ruby because I wanna make more advanced things.
For the front end stuff, you linked the PR that adds an outlet on the user nav.
But is this the only way to add content to the forum?
Would it be possible for example to just add a button somewhere on a user page that links to a sub page for a user?
Might be a bit vague but basically I’d just want a /users//stats page or something and render custom data on that page but still have the user header and such.
So it’d be something like this with custom content in that blank space.
Thanks for that link with tips and tricks btw haven’t read it all yet but it seems like a good place to start.
I’ll just go read some more ember and ruby guides.
I thought most of this stuff was Discourse (API) but seems like most of it is just Ember basics.
Thanks once more for all the useful answers. 