Travel costs to look at other properties.If you travel but have not identified the property that you want to buy yet, the cost is considered an investigating cost.

And while nothing is foolproof the most consistent method of finding good vendors is relying on OTHER real estate investors that have worked with those vendors. 

I don't expect to know everything by then, but I hope to develop a basic strategy that prevents me from making the most common and costly mistakes that a newbie can make.

What are the best methods to independently verify zoning and land use data to ensure compliance with local regulations?

Can try to reposition to Class B, but neighborhood may impede these efforts.Vacancy Est: Historically 10%, but 15-20% should be used to also cover tenant nonpayment, eviction costs & damages.Tenant Pool: majority will have FICO scores of 560-620 (approaching 22% probability of default), many blemishes, but should have no evictions in last 2 years.

My method has always been to call every listing that hit 90 days on market in areas that I want to buy.

What's the highest success percentage method to find a previous tenant's new address for this? 

You definitely want to use a thorough screening method like rentprep.com that gets their income, credit, background check, and call at least 3 references (make sure to verify them by address/job and then their name).  

Some have used this method to obtain 100% financing.

Depending on how the water is getting in, there may be cheaper methods for sealing the basement walls from inside.Keep shopping until you find someone trustworthy with solutions.I would also consider going after the first contractor because they robbed you.