[DiapDealer]

Also note that if there's any intent to use the epub to convert to the Kindle format, the fonts absolutely can't be obfuscated at the time of conversion. The Kindle distribution platform obfuscates ALL fonts (using their own scheme) before delivery to customers.

With regard to your Sigil crashing issue; if you happen to be using OS X, consider deleting your Sigil.ini file. I have no idea where it's located on a Mac, but there's lots of threads about Sigil crashing on OS X that were solved by deleting that ini file before attempting to restart Sigil.