I am still leaning toward the holding company, but mainly for anonymity and passing assets down to my children.

However, since most of your assets are jointly owned, a single revocable trust might be simpler and more convenient.

We don't have kids yet, so we knew this would be the most comfortable/convenient time in our life to house hack.

STRs also make for a convenient scapegoat for the government when they need to divert attention away from their own policies that make adding more housing units more expensive/time consuming. 

It's the in town STR properties that aren't particularly convenient to any of the major attractions that have struggled the most since this market became crowded.3) The difference between good and average or bad STR operators is huge. 

We were planning on selling it but are leaning towards keeping it and using the BRRRR method.

Columbus, Ohio is a great market to consider if you are leaning towards that appreciation.

Like @Jeremy Holden said above, sub2 could be a good option for you, he's a great resource to lean on in this market as well.

Currently leaning towards the ADU idea.

It was just convenient.