Are 2 GT 710 graphics cards enough for deep learning? I want to do some kind of complicated deep learning (specifically, https://github.com/Sentdex/pygta5/), but I don't have a decent graphics card. I am willing to get 2 gt 710s. Are they enough for this purpose?
No, it appears to take large amounts of screenshots to generate the images to be used for training.

Don't waste your money. I would say you could try training on Google's colab if you can upload the training data.