If choosing to sell the DADU, did you split the lot or is this wrapped into condo-izing the home and DADU? 

Rates will be 10-13%, depending on the terms.A HELOC can be a good tool to leverage your equity for a down payment without touching your current low-rate mortgage.

Choose that one and use it.

That's not to say all properties will as it's very dependent on the property and the investors situation.

Ultimately, it depends on your goals and the opportunities available for investing your wealth. 

You learn the most about being an agent in the field and by choosing a good first brokerage with good training either in-person or online, depending on your preference.

SO depending on your situation that might be the case as well!

Best to involve attorneys/lawyers as well, but it depends on the type of financing you get.  

Whether you classify it as business or personal income depends on the nature of the lending activity.

Most of my renters choose #1 because it provides a clean break.I document everything and I don't accept the early termination notice or start the clock until they pay the termination fee.