Assuming the tank is cycled, and since you have live plants, you could add new fish any time. The temperature must come down to 76-77F for panda cories. A couple degrees may not seem much, but to the fish which are ectothermic it is very significant. Temperature drives the fish's metabolism. Panda cories also like some water current, more than any other species of cory I have so far encountered; cardinals by contrast prefer quiet or still waters.
A note of caution on the dwarf gourami...unless you can obtain this species direct from the breeder, or can verify the breeder, they are best avoided. The iridovirus which is not treatable is a risk with poorly-raised dwarf gourami; this species should never be acquired from chain fish stores especially. The Honey Gourami would be a better option if you want something around that size.
And, welcome to TFF.
Byron.