1) Ya gotta know your Limitations.
Do what you are good at. Get help with the rest.
(And for goodness sake, get more than one set of eyes on the work and ask for constructive criticism. IMHO there is no excuse for wrong words or bad regional spelling. A
Yes man does you no favor. )
2) e-books are not Print Books. The versions (layout) may need to differ for a number of technical / $$ reasons .
3) Web page HTML are different beasts.
A brilliant Web designer will probably be a disaster with EPUB . KISS whenever possible (at least till you are established). It needs to work on many devices that all have their limits and quirks.
Can an Author make great e-books? Absolutely (some even hang around here
).