Welcome to the forums, and congratulations on that incoming K-1II (
very nice!
)
I'd recommend you have at least two, and preferably three or four batteries - that way you can shoot with one in the camera and always have a spare with you, but also one or two more on charge. It really depends on how often you're shooting, and how much you shoot in a session. You might get away with just two if you're not regularly running out of juice. Perhaps start with two and see how you get on?
As for lenses, despite what a few folks might say both here and on other forums, you're pretty much spoiled for choice unless you're looking for something quite extreme. A lot of folks here use the
HD Pentax-D FA 28-105mm F3.5-5.6 ED DC WR as a general purpose lens on full frame, and it certainly seems to deliver nice image quality. It's also pretty inexpensive considering how versatile it is, and the weather resistance capability.
Good to have you with us