I think her disappearing is due to her being a cosplayer. She seems to love dressing up in Star Wars costumes, I'm betting that she also makes money from it. She's likely not ready to tell the MC about it yet, as she's probably afraid of what he will think of it. She doesn't know about the pictures that Bob has been sharing with him, but him seeing the pictures of her dressed up in her room could be the first step.
I'm not sure if I can see Devon working at the Pink Box, but maybe like you said, when the MC takes it over if he asks her to help him?
I wouldn't take too much notice of this promotional picture though of the game. It may happen and it may not. That outfit looks incredible on her though.
The bartender is Ella, who we meet at the cafe. She is Lola's sister and we often see her sat by reception on her laptop.