What maintenance should I do at 100k miles?

The valve adjustment is the one people skip and it's the most important on a Honda. The K24 engine has solid lifters (no hydraulic self-adjustment). Over time, exhaust valves tighten as the seat wears. A tight exhaust valve doesn't close fully, loses compression, and eventually burns. I've seen K24s need head work at 150k because the owner skipped valve adjustments. It's the single best thing you can do for longevity on this engine.