For the Parrots or different fish? It all depends on your fish, if you have a nice big school of Tetras and a school of Cory catfish you could feed once a day just fine. A pinch of flakes and a high quality veggie wafer for the cory cats. You can even feed them actual veggies like raw cucumber. Some people suggest to blanch the cucumber but my cories/otos/plecos always loved it better raw. Just cut up a slice, weight it down with something like a rock or a fork and let them at it! The first time you do that, they might not find it right away but if you keep putting it in the same spot each time you feed, they'll know where to find dinner ^_^
Plants, I definitely suggest plants! Live plants is a very different story and if you want to tackle them, you'll need to do plenty of research of plants and of lighting fixtures. But you can use regular fake plants. I do still recommend silk/fabric plants over plastic plants as plastic plants can cut up fish fins and that's no good! So lots of plants of all sorts and some nice hiding places like you have now. The one is good but two or three is better
I know this is all a lot of money but fish keeping isn't cheap, I'll say that right now. If it is possible, can you find the Parrots a different home? Maybe someone who already knows and keeps Parrots or bring them back to the store? You could sell them too, I'm not trying to get you to just give them away since you did pay money for them and all!
I hope this helps and please ask all the questions you need, even if you think they are silly! Any question is valid ^_^