How can I add H5P content to a Lesson or Book?
See the section 'Embedding H5P' in H5P for details.
How can I ensure that the grade from the H5P content is stored in the gradebook?
You need to use a H5P activity rather than embedding the H5P content in a different activity.
Can I migrate content from the mod_hvp plugin to the H5P activity in standard Moodle?
Yes, with the H5P migration tool.
Is it possible to import H5P question types into the Moodle question bank?
Yes - for some (though not all) H5P question types, using the H5P content types format plugin.
How can I make sure that my H5P content is accessible?
Please see the h5p.com documentation Recommendations and overviews of content types.
Is it possible to style H5P content the same as the rest of my site?
Not yet, though it has been requested. See MDL-69087.
Any further questions?
Please post in the H5P forum on moodle.org