Liveaboard first time

First time doing multiple dives for 7 days. Friend said to bring my freedive long fins for snorkels. But I know you can’t dive down after scuba diving far - is this correct? I don’t want to feel peer pressured into possibly getting DCS after dives for freedives. I’m not a freediver but have long fins for occasional fun swims I’ve done in the sea. She’s more advanced but again what are the risks and what should I avoid? Also how long should I wait after the liveaboard to safely fly back? Thanks!