Covers, WhisperSync and Custom Fonts

[sillystuffs]

I converted EPUBs to MOBI (using the setting 'Both') and used 'Send to Kindle' Desktop app. It did not have covers in my Paperwhite but I was able to change to Custom fonts and they were syncing between Kindle on Android and my Paperwhite just fine. Now they don't sync anymore. Whispersync settings are fine because books that I got from Amazon and Kindle unlimited are syncing just fine. Problem is only with Converted books. Can you please help me to identify the probem here? Following are the requirements in their order of precedence:
1. Books should be available on cloud
2. Whispersync should work across devices
3. Ability to use custom fonts on Kindle Paperwhite
4. Display book covers on Kindle Paperwhite

What should be my conversion setting?

Thanks for your help!