The grass in your game worked really well, I think I even noticed it growing back.
Regarding SFX, I try to make all my own assets. For this game. I made everything apart from the font (Fonts are quite complicated and require the correct software to make).
I know I'll get to a point where I'll need to use assets from other sources, but there are so many different licenses and conditions, that tracking them all, and any changes, is job in itself.