Historically, many lenders will not exercise the due on sale clause even if you violate it, but it is within their right and they may do so at any time.

You can of course improve this general rule of thumb by:1) putting more money down to lower your monthly payment2) buying down your rate to lower your monthly payment3) get a cheaper insurance quote to lower your monthly payment4) use a different product with a lower rate for a lower monthly payment like a 5/1 ARM FHA5) if you're in a historic district you can apply for property tax exemptions which lower property tax and thereby lower your monthly payment like in Orange, Ca they have a Mills Act which reduces the property tax to about 1/10th of the surrounding properties.

What can they give me in terms of data--rent history, leases, repair history, their fee on the property, historical turn and fill rate, avg length of tenant--all that kind of stuff.

Historically, I have invested mostly in the stock market, but I've really spent some time learning more about RE investing, specificallly on the SFH and small MF side, and I'm thinking this would be a good place to deploy some of my capital (if done correctly of course!). 

I won't be investing in the riskiest/most supportable asset subclasses such as hotels, and tilt my portfolio the ones that have historically been more stable such as multifamily and single-family housing.

What method would you use to find historical rates or predict the future property tax?

Call the utility companies to get historical records for anything that is owner paid.3. 

I won't be investing in the riskiest/most supportable asset subclasses such as hotels, and tilt my portfolio the ones that have historically been more stable such as multifamily and single-family housing.

Competitive Market Analyses, different types of historical sales data, agent notes are the ones that come to mind.

You're looking at historically low cash flow/high appreciation areas and predicting low cash flow.Where are you getting -3% from?