I'm curious to know the policy on attaining buildings that are inactive yet still owned by others. (The Wench's Clench or The Dirty Nancies Gambling Hall) I also would like to know if it's possible for me to build or expand buildings. (Like make a secret tunnel underneath said building or have Wally the Shipcrafter make a ship for me.) I'm pretty sure this will all recquire money. But I'm pretty sure I need help from the DM's to attain any of this.

It's all possible, but would indeed need to be achieved IG with a DM overseeing.