Yes, those are adapter types.
Close. Distinguished fields are only used to make accessing data in messages
from orchestrations easier using the <message>.Field syntax. Property
Fields, on the other side, allow you to write data to the message context
(either data coming directly from a field in the message's body, or
arbitrary data like the adapter properties do).
MIME/SMIME is an encoding/encription mechanism typically used in dealing
with EMail encription (though not necessarily so). You'll only need to use
it if you know you're getting MIME/SMIME encoded messages or need to send
them to someone else.
As to how you know, well, someone tells you :)
Certainly there are messaging only scenarios, but most of them do use
pipelines (they are necessary for many purposes), even if it's only the
built in ones like XMLReceive or XMLTransmit.