Hi
If I buy graphics and game assets from themeforest or other sites and make a 2D game.
:: How much I can earn in one year?
:: How much it downloads when publish in googleplay in one year?
I need a average 
Why don’t you try your self? Your question seems silly, but I try to answer you.
How much you can earn? 0 - 1m. Average is 500k. (??)
How much downloads? 0 - 10m. Average is 5m. (??)
it’s not exactly answer
but what’s your nitch but for me the best apps that earning 7$ to 9$ per day