If you're really public about it in-game (shout chat, duty finder party chat, yell, etc.) you may run afoul of RMT rules and community attitudes.

Most of the FF streamers I play with cultivated viewership through FF community discords that permit advertisement, and random viewers simply clicking into their streams. Many do 'charitable' community activities, like hosting learning parties and in-game events, where it's a little more acceptable for them to do a bit of self-promotion.

There are also FCs / Communities that are composed of lots of small streamers that typically allow their friends and members to self-promote their streams in the FC/community discord. Befriending other streamers can be a pretty quick way to grow viewership, and will help you populate events and parties when you get around to hosting them.