hostname to point your purchased domain name or a host name from the domain (in short or long form - depending on the hosting).
as the IP addresses indicate 1XX.XX4.XX.X55.
probably so, but not a fact. still, when setting up domain zones, there are well-established terminology - a-record, AAAA-record; and in your question nothing about them.
a screenshot would give more insight, but, alas, no.
Reverse DNS is the reverse area; in contrast to direct, which is used in order to obtain the IP in response to the request of the domain name, the reverse is used to get domain name on IP. used rarely, but neatly. in your case, I think you can not pay attention to it until unless you hit that you need it (for example, to keep the mail server).