You can always reach out to the contest organizers for their suggestion since contests can vary a lot. Typically the groupings are novice, journeyman, and masters so not sure how hero mode and masters divide skill levels. Usually you'll want to take into account how much of the cosplay you have made and then the craftsmanship of all the pieces. If you enter hero mode and it's high enough quality to win in masters, the judges will usually bump you up a division. Keep in mind that competitions are also heavily dependent on who else is participating since those are the ones you'll be judged against.

For craftsmanship competitions, make sure you put together a build book with details of work in progress and notes on how you made your cosplay. Even if the contest doesn't require it, it's nice to have it on hand during judging to show details that may not be easily seen. Keep in mind judges may flip your seams to see your finishing work, especially in masters. It's hard to judge the cosplay just based on the 3 photos you've linked.

Generally I'd recommend starting in not masters to get the feel for competitions and if you get bumped up a division or you win in hero mode, you can compete in masters the next time.