The file validates with Flightcrew, and the font files size is reasonable, so I guess it would work fine in readers that support embedded fonts.
But note the <meta> tag for the cover points to an id that does not exist in the manifest. Since <meta> tags are optional and can contain everything, Sigil will not touch them and they don't affect validation. Also, some fonts seem to be unused, and you might consider specifying the font only for the Cherokee script fragments, and not for the English text.
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