Count isn't the metric. Job coverage is. A service page earns: one strong real photo up top (your crew, your work), two or three supporting shots (process, before/after, finished results), and nothing that exists purely to fill space. Every image costs load time; make each one carry proof.
Real beats stock, always: customers can smell stock photography instantly, and it converts like the wallpaper it is. Phone photos from actual jobs, lit decently, shot horizontal, outperform purchased perfection.
The technical hygiene: compressed files (under ~200KB each), descriptive alt text ('technician replacing electrical panel'), and dimensions set so the page doesn't jump while loading. Speed is part of the design.