I checked with Santa Clara County Weights and Measures about 4 years ago for the same reason and they stated there was no problem or need to comply/register/etc. to sub-meter tenants from their perspective.

What are the best sites to monitor housing data like this and others?

@Joe Gore @Phillip Dwyer @Scott Pigman   Joe your In the 1960s  times they be a changing.read Phillips response he has it laid out how it is.. the new lock box's can be programed to only open at certain hours and certain days and you can also access them with your I phone app. . .they will send an e mail to the owner of the lock box ( agent)  the minute another agent access the box .. they are really pretty incredible and depending on the agent very valuable tools to monitor showing's.

It's a matter of weighting the pros and cons.

Monitoring this topic can't wait for updates! 

Yes, the WAY, weighted average yield, for the net yield, look to the weighted contribution of cash and leveraged funds to the total.

But ultimately, I'd like a lot of this information to be tracked and easily reportable so that I can monitor my progress and refine it over time. 

You can monitor any lien activity by logging in to check your account.

Cash has weight but not as much as investors think.If my seller wanted a cash buyer in that instance we would simply reduce the price down until we found one who would pay a premium.Example from 3 mill to 2.9,then 2.8 etc. and get cash at 2.7 to 2.6 instead of 1.8.ORThe seller could do a wrap with 20% down and sell for a much higher price.If you applied the 50% theory in some areas the property would be gone in a few hours at those levels.50% is like hitting a grand slam when most hit doubles.Depending on the area the 50% theory does not always apply.It is simply a guideline where other factors have to be taken in.

We also hired a next door neighbor to do it for awhile; you would need to monitor quality.