i've been using the software for a long time, i made "megaman sprite game" with it 10 years ago! the game was made as a little side project that I worked on infrequently, so it took 6 months from start to finish but i wasn't working on it a lot during that time!
you can't delete maps unless it's the most recent one, but you can delete everything about the map so it's restored to a blank slate. I think it's in "delete map data" or something but I can't check because i'm away from my computer for a few weeks. as for transporting heroes, you can simply use doors! if you need any more help i recommend signing up for the Slime Salad forums or discord or consulting the OHR wiki