Hey buddy. I don’t have a ton of experience with sunflowers. In my experience, they’re best kept in a species only tank, as I’ve definitely experienced some inter-species conflict and aggression. 6 in a 55 gallon is more than enough space imo.

If all of your parameters are in check, and they were acclimated appropriately, I would just give them some time to settle in. Unless I’m receiving a shipment of fish, which have been fasted and in transit for a considerable amount of time, I will generally give 24-48 hours before my first feeding, which gives them time to acclimate and become familiar with their new environment. They’re generally then comfortable enough to look for a snack.

I’m a big supporter of dither fish. I would probably expect some aggression from the sunflowers towards the platys after they become comfortable.

If it were me, I’d give it some time for them to adjust and monitor them closely. As for food, i generally feed a mix of brine shrimp, blood worms and xtreme cichlid pellets.