Can you please help me choose the right airsoft BBs for my gun?

I'd recommend a happy medium. Go for the .2 you get a little more weight for accuracy but yet light enough for a little more range. You want good accuracy and range for airsoft. Unfortunately with spring powered your not going to have much in either unless your within 20 to 30 feet. I would start looking into a Co2 powered gun. 12 gram Co2 cartridges are actually pretty cheap. With Co2 you get a lot more velocity range and accuracy. Another thing I would look into if you like the rush of airsoft is paintball. Most importantly just experiment and find what works best for you and just get out and have fun.