I wonder if I'll acquire more poke balls over time or if need to buy them.
It's gotten a little rough. Once I hit level 6, the Pokeballs became few and far between. In the DS/Game Boy games, you have to grind and battle lots of wild Pokemon so your team will be strong enough. In Pokemon GO, it's a physical grind: I walked/biked to the PokeStops in my area for two hours today just to get enough Pokeballs :/
Nevertheless, just when it seems hopeless, I level up again and receive 15 more Pokeballs. I can definitely see the appeal to buying Pokeballs, but I'm going to stay strong, and earn my Pokeballs with sweat! (and time, a lot of time).