For sunset exposures, use a hand-held meter to either incident+average several areas (light and shadow) or spot meter them, then extrapolate the readings to the pinhole.

Star trails are easy enough with an SLR in Bulb (with the requisite knowledge of where to poke the camera into the sky for the best results!), but a pinhole has extreme depth of field thus exposures are very, very long, maybe around 8-12 hours, and then reciprocity failure must be taken into account. No separate meter will assist there — it needs experimentation. Choose a field that is remote enough that curious individuals will not approach the camera (nor for that matter animals that wander in the night: in Australia, kangaroos are a persistent problem, bumping into the tripod!). A fast film (400-to 800iso would help), but at a basic level only a fair bit of trial and error will determine what works best.

In the early southern hemisphere Spring I will embark on some experiments for star trails with my Zero Image pinhole and Provia 100F (same as with SLR star trails capture).