Hello!

[Worldtree]

I have 2 at the moment:

-Is there any sort of sandbox where I can work on drafts?

Yes just post a new thread in the forum section “Encyclopedia galactica articles” 
or “general discussion” . It’s helpful to talk about your idea first before writing up a draft of course, much like the SCP foundation process 

-Is there any sort of "greenlight" system for new authors to recieve approval regarding their first post?

I approved your first post on the forum just now , before replying to your greeting , to make you post visible to everyone else (it’s an anti spambot measure) so that’s all set if that’s what you mean. All of your posts on the forum from now on don’t need to be approved. 

The process of publishing an article here is a bit more centralized than the SCP foundation system -there’s not a formal voting system exactly 

Describe your idea for an article or story , maybe talk about it and troubleshoot it with other posters here

Write up a draft 

Posters here comment on your draft and you probably rewrite it 1-6+times 

One 1-2 editors/administrators say it’s ok to post on the site and there are no objections, one of us editors will post the article on the website