Adventure Time started as an animated show, not a comic. The TV series gained popularity before any comic adaptations were made. The animation was the initial form of the story's presentation to the audience.
Adventure Time has been at Comic Con on certain occasions. Usually, it's part of the event when there's new content or special announcements related to the show.
The Adventure Time comic is canon. It adds depth and new perspectives to the existing storyline, while adhering to the fundamental framework and lore of the franchise.
The change in sex comics could be driven by legal regulations and the need to adapt to different markets. Sometimes, the artists' own creative evolution also brings about changes.
Hard to say for sure. But the Adventure Time comic has a way of resolving relationships in interesting ways, so there's a chance FP and Finn could reunite.
As of now, there doesn't seem to be a second Adventure Zone comic. Usually, announcements for new comics come through official channels or creator statements, and I haven't seen anything like that for a sequel.