Since I understand it can vary widely based on the variables you mentioned, maybe you could provide me with some common red flags that relate to these items that may get some people into trouble. 

Read Rich Dad, Poor Dad, then shop the wide range of books on BP.

Are there any great examples of cities allowing ADUs more widely with sensible zoning and positive impact?

Triclosan has shown some alterations to bacterial structures, but it is not as widely available any longer.Triclocarban is very common and highly antimicrobial but again, there isn't a lot of data about long term resistance.Anyways, a typical human is exposed almost constantly to viruses, bacteria, phages, fungi etc that you really don't have much of a chance of not building up immunity over time.

These are important:1. basement has water leaking into it in 2 areas. contractors tell me its coming from the footer and getting in. i dont quite believe it. i have 2 plans to figure this out. im going to dig a deep hole outside....about 2 inches wide...as deep as i can...and see the standing water is. ive also thought about getting someone to drill into my concrete blocks inside of my basement to see if water is setting in the blocks.

Do you try to cast a wide net, then evaluate which is most profitable/logical for yourself and then dive more into that?

Eyes wide open.

Get referrals and have a wide range of questions to ask.

Investment risk can come from many angles.

But there shouldn't be two people working it from different angles as it causes problems.Just my thoughts and Good luck!