Hello Rolando,
I would tend to avoid fixed layout
books if possible since they can be hard to read on smaller
devices, and they're generally harder to get right. While Jutoh
does kind-of support them, when the text isn't hard-wired into the
graphics, Jutoh can be imprecise in mapping from the editor to the
finished book (editing at a high resolution can help mitigate
that). Some people have success creating fixed layout books with
Amazon's Kindle Kids Book Creator, or you could even try
submitting a PDF. But if there are large portions of text done as
fixed layout, it probably won't be an ideal experience.
Re. text size, if creating a reflowable
book, I would recommend simply using the default text size for
body text (12pt means 'standard text size' to Jutoh and is
exported without an explicit text size). This allows maximum
flexibility/accessibility for the end user.
You could definitely add panels as
images to a reflowable book, although there will be margins that a
fixed layout book wouldn't have. Kindle will allow zooming into
images though not in the more complex way possible with a fixed
layout comic book.
Regards,
Julian