I'd advise wrapping Hebrew-in-English in spans with the dir attribute set to rtl. I'd also advise following each span with the lrm element.
As for fonts, pointed Hebrew support is now surprisingly good in the default fonts on a variety of platforms: Kindle Paperwhite, Kindle for Mac, Kindle for PC, Kindle for iPad, iBooks for Mac, and iBooks for iPad.
One platform completely lacking Hebrew support in the default fonts is Nook GlowLight.
So, see if the platforms you care about have okay Hebrew support and, if they do, consider just letting the default font be used rather than providing your own font. Providing your own font has its pluses and minuses.
For more detailed help, I am available professionally: http://bdenckla.github.io/efs/.
P.S. I consulted Meta Stack Exchange about self-promotion,
and I hope I understood correctly that it seems it is within community standards to have promoted myself as I have done above.