AquaMail may not have an option to prevent the floating compose button from hiding after scrolling down. Also, AquaMail may not have an option to mark an email as "Important" like Gmail. Regarding conversation view, you can try changing the settings in AquaMail to show all emails in the conversation. To do this, go to AquaMail's settings, then to "Display and Layout" and then turn on the "Show all messages in thread" option. This should make the conversation view look more like Gmail, with all messages in the conversation shown in the email chain.