9 Kingdoms 2017

I'm ready to play in a single or double elimination tournament – it doesn't matter.

Regarding the tournament – based on the theme, the most optimal option seems to be the one used, for example, in Dota 2:
invite 8 popular streamers (direct invite),
the rest – all those who want to participate – go through qualifications until 8 more players remain. Qualifications without mandatory streaming.

However, the qualifications might take a long time, because Dota 2 uses a qualification system where "everyone plays everyone" in several groups, and then there's also a double elimination. In this situation, it means that the qualifications will last longer than the main tournament (about three times longer).

Added 15 minutes later
In my opinion, it would be easier and faster for the tournament organizer to limit themselves to direct invites, as, for example, twaryna did in the Show Tournament for HoTA.
And yes, I recommend creating a regulation for templates, rules, etc., right away, rather than in the style of "everyone does as they want, and we'll agree later." After all, it's up to you to decide what kind of tournament you want, at least in terms of the duration – fast (M200) / medium (L+U / JC) / long (XL+U) / mixed. And I would recommend using the most popular and proven templates from each category (I think everyone knows them).
It's better to create the rules first and then make changes if there is general dissatisfaction, rather than inviting people to participate in something they don't understand...