Thanks for all the pointers.
To summarise, obfuscation is required by some font vendors and not, as I thought, by whoever sells an ebook to the reader (Amazon, Apple, B&N etc). So these vendors are "out" if it's not a general requirement.
@JSWolf: I just learned today that subsetting (or modifying---as in fixing---things like kerning) is not permitted by some vendors. These are out, too.
A current discussion on
Hacker News (https://news.ycombinator.com/item?id=28403484") talked about this and other license issues that made me come to the conclusion that apart from Public Domain, SIL Open Font and comparably licensed fonts it's just not worth the hassle picking apart lawyer created legalese. List is getting really short now.
That leaves just a handful of font vendors (plus free fonts, OFL, Google etc). I like the Fontspring approach, but their catalogue lacks in some respects (which is probably me having the wrong taste).
@jhowell: Thanks for the examples to look out for when subsetting. I would have tripped over ordered lists (but left all the ligs unchanged just in case). Btw: I believe inserting a "zero width non joiner" prevents many (all?) renderers from showing a ligature where the zwnj is meant to force two individual letters. But I haven't checked this with the latest KPV as I had some other rather silly alignment issues.
@Tex2002ans: In the end I'm not even sure if I will subset at all. I tend to use small fonts to avoid bloat anyway, but the final decision depends on a few tests I'll have to do to see how much fonts can be shrunk.
Thanks again folks.
klaus