Splitting before the meter is likely not an option unless you want to pay for a new service with your water utility. This is often thousands of dollars.
I'm not familiar with Tennessee primacy regulations on water so we'll go off Federal standards (your state will meet or exceed these). You have at least 20 psi coming through the water meter to the property (but probably at least 50-60psi) which is ample for what you're doing. Flow is often a bigger problem for things of this nature but, as said if you connect to the greatest sized line you can find, it shouldn't be a problem.
The cost of an effective water meter for what you're doing is going to be a couple hundred dollars. You don't need anything fancy, a small (5/8-3/4") positive displacement meter will do what you need and should last well over ten years. By teeing off the immediately effluent side of your property's water meter box and metering yourself there, you're going to have the most accurate readings (meter1-meter2=tenant usage) and least amount of flow restriction as well as the minimum impact on one-another's supply during use.
However, to be legal, this will likely need a permit and to meet some basic standards (bury depth, materials used etc).
DIYing this isn't hard though, and would not cost much to do. Full line+meter+fittings to the outbuilding should be $500ish. That's assuming you own a shovel. =)
