The SP1000 is my favorite Pentax; I've had two and gave one to my brother in law, the other my daughter stole.
Question: why bother using the K1000, the SP1000 is fully its equal (some might say the guts are indistinguishable) and gives the benefit of using M42 lenses in 'native' mode - i.e. with auto diaphragm action at shutter time?
Buy a couple of cheap M42 lenses for the SP1000, and you'll have an incredibly capable and cool outfit for next to nothing. That's the business case for screw mount
The 55/2 is an excellent lens - it is the exact same lens as the 55/1.8 but with an aperture limiter. Evenly sharp across the frame and across the apertures.
Batteries - I use modern batteries without any problem at all. I bought some "S400PX" 1.55v silver oxides made by excell.