cant give you a definitive answer since I don't work for tiktok, but as I understand it your goal is to train the algorithm to find the perfect avatar viewer for your content.
This is done by consistent posting with a consistent theme using relevant hashtags.
The algorithm generates a test audience and based on the strength of those responses largely weighted in favor of things like completion rate, accumulated watch time, saves , shares and comments. If this reaches some threshhold then the algorithm will "guess" at a bigger possible viewing audience and keep doing this until the post dies or keeps getting stronger positive signals.
The more your content can be understood by the algorithm in terms of something it has pre-existing data on the easier will be to find a bigger potential audience.
The more content you post, the more information the algorithm has to refine a possibly interested viewer.
-You are doing decently if 1 to 2% of your viewers become followers at least at the beginning.
-Promoting posts is most likely a waste of money. Viewbotting is also most likely a waste of money.
-there probably is some element of luck involved in growing an account.
Don't take my word for any of this as I have only begun to put any of this into practice myself. This is just the available information I could find on the matter.