Yes to all three questions
How?
The linked topic describes how to compile neomutt with Autocrypt support (in Debian), and how to enable Autocrypt it in neomutt’s config. The post says “it doesn’t work”, though. If it doesn’t work with neomutt (currently), what made you believe the answer is “yes” to all three questions? Did it work with some previous version of neomutt?
Is it implied that enabling Autocrypt in any MUA would be enough to communicate with DC users, or are there other requirements? (the linked topic only discusses Autocrypt)
How could DC user (person B) having a chatmail account make the first contact with email user (person A)? In DC (android) I only see options “share QR/i.delta.chat link”, not send an email (when using a chatmail profile).
How could email user make the first contact with DC user? Should they simply send the first message (plaintext with Autocrypt header) to the email address visible in DC settings?
E-mail is increasingly concentrated in the hands of a few oligopolist providers
just in case, clarification: in the scope of original question, both person A and person B use non-oligopolist non-evil email providers that don’t reject private servers, work on solar energy, and smell like roses. 
