Op ex ratio may end up being more like 45% or perhaps 40% with newer high quality construction.

Not the case.Just like everything else, there are always different quality of Section 8 tenants.  

Also, not very easy to use typical methods of valuation like comparable sales - there is no public tax assessor's website that you can just freely grab this from. 

Also, it often helps to connect with a local agent/do extensive due diligence on renovated/new construction properties to see what the property may sell for or appraise for (if doing BRRRR method) as that can impact the price you should pay.

Does anyone have a template or method that they use in order to screen tenants effectively in order to reduce the risk of non payment and damage to the property? 

Since you aren't looking at the BRRR method, I am assuming you want something that is turnkey.

While I don't object to spending money to do one's due diligence, I don't know if $500 is called for when you can get very high quality syndication groups/meetups/information for free.

I suspect, as more and more leasing-related disputes are occurring involving credit cards, the companies have already figured out their method of handling these claims.

Quality VariesNot all coaching programs are created equal.

These methods include: Detailed Engineering Cost ApproachDetailed Engineering Cost Estimate ApproachSurvey or Letter ApproachResidual Estimation ApproachSampling or Modeling ApproachExperience or “Rule of Thumb” ApproachIt’s important to understand the differences between the approaches including which one best fits your property and the reliability of each approach.DETAILED ENGINEERING COST APPROACHThis approach compiles the costs from construction and accounting reports to build a report.