Would give me practice to rent it once I move out etc. 

It is a very beginner-friendly, pragmatic guide to good financial practices. 

What are the best practices for quickly securing reliable tenants and ensuring positive cash flow, especially for someone new to this?

Good to see the city make some practical decisions.  

And yes, over leveraging a Subto and using "gator" lenders is not only bad practice, but it's going to lead to law suits.He is wrong on so many levels that I have posted extensively on it and it gets boring.

I'm sure there are agents and investors with deeper insights, but for most of us, a consistent, long-term approach—similar to dollar-cost averaging when investing in index funds—seems like the most practical strategy.That being said, I am also interested to hear what others have to say though, so thank you for the post!

- What are some best practices we should keep in mind to keep maintenance cost of the ADU to the minimum in the long run?

Your desire for control and liquidity are likely the two biggest assessments you need to make first, as this will start to narrow down your choices very quickly.

If it is working with subs, a GC license won't help that in any practical way.At the end of the day, it depends on what you are looking to achieve.  

Maybe a family in your area has a relative that would like to rent nearby but who doesn't think now is a good time to buy in this current housing market.You might even find someone who likes to target practice if that's a safe activity in your area.