I prefer no indents at chapter start - but if they are too much hassle to fix, I let them be.
e.g. sometimes there's header line, then some more spacing, then start of chapter which makes for a hard to detect combo.
I also prefer to see no top margin ( =wasted e-reader screen space) above the chapter header, & for the chapter header to be centered, and not huge - 1em is usually sufficient.
May I ask - the h3 + p.calibre9 construct will apply css to only a <p class - ... line which immediately follows the END of a h3 line ?
where can I find more documentation on building compound css definitions such as this please