How to water is going to depend on your exact climate, Guest. Along the Gulf Coast, it may need very little extra water, except in drought years. West of the Pecos, it will probably need a deep soaking every 2-3 weeks in summer, possibly more often in very sandy soil. About once a month in winter. In the hottest parts of the lower Rio Grande, once a week soaking is common.
Division can be difficult, between tangled fibrous roots, and tough woody rhizomes. Sometimes you can get away with the "two pitchfork" method, but more often, you will need an axe (or a machete!) Either way, you will need to cut off about 1/4 to 1/3 of the leaves, starting with the oldest ones, to help keep it from going into shock. In USDA zone 9 and warmer, the best time to divide is the fall. In zone 8, spring is somewhat safer.