I’d be curious how accurate your tool is with a comparison to real-world deals after they are sold.

Wherever you took your broker's class you should have ample study materials.If you are talking about your real estate agent's license in NJ (that is not a broker's license), you need to take the initial class at an accredited agency and they will give you all of the materials after you finish the 75 hours for the test. 

Are you using a specific property management software to handle this automatically, or do you have a different system in place to ensure accurate tax reporting?

@Alan Asriants this is accurate and thorough.

Now the post test reveals I have pvc sewer line leaks under the concrete foundation. plumber has found multiple breaks in the line which need to be repaired and has provided an estimate for tunneling under the house and replacing entire 45ft main line!

The fact they told you this through customer service makes it seem pretty accurate. 

If the fan is working the system is almost certainly functioning.There are very cheap testing kits that involve opening them and placing them in areas likely to have radon. 

I have about 250k USD to allocate to this venture, but I may want to dip my toes into the market with a single-family residence in an area like Parma Heights and test the waters.

Quote from @Scott Trench: We just are testing it out!

Testing itself costs $350+, and the follow-up testing costs another $300-$400.