Krismo962
has given the best advice and I totally agree to it. Almost Everyone here has done the mistakes they are warning you about. I urge that you make mistakes, just be careful enough to not kill the fish. Keep the fh in the 55 until it's not cramped and I'm sure until it starts to feel cramped you'll have enough attachment for the fish that you'll either get a new tank or rehome it to a better place. 
I’m finally in a spot where I don’t need to stress. The FH is in the 55 and the 40 is in the living room. Flower is alone in 55 and don’t need to worry about it other than feeding and water change
Don't stress out too much ?
My moms frogs and after the tetras pass away I’ll be adding some type of small cichlid. Not sure about any dwarf cichlids or if they’ll even be suitable for a 40g. But that’s pretty much all
I added 30 gallons of pure spring water treated with bio booster and conditioner along with 20 gallons of the water from the 40g. Got all new gravel added old filter media’s into the box of the filter and old decorations. The FH is already in the tank and daisy is loving all the space to himself
These two have been housed with tetras and Cory cats their entire lives and never had a problem
