6mm
airsoft uses 6mm bbs. Perhaps you are talking about weight? .20 gram is good.
I haven't bought an airsoft gun from this web sit. It cost $25 and looks legit. But i don't know it seems to good to be worth it.
The objects you place on the field should vary according to what size the field is. But you can put whatever you like out there as long as you can get it there. Just make sure if you are going for at least some level of realism, to place objects as they have some sort of purpose instead of just randomly scattering them about. Also it would be a good idea to keep the sides of the field balanced somewhat so no one team has a crazy advantage over the other
No.
6mm
If there's varying sizes of airsoft pellets, then each size will only work for airsoft guns intended to take that size pellet. Others will be either too small or too large, and could end up damaging your airsoft gun, or even getting stuck in the barrel.
BB's for air guns (NOT airsoft) only come in one size .175 commonly referred to as .177 caliber. If you want to know about airsoft BB's then you need to put the question in the "Airsoft category."
No it depends, you need to check the rail size of your rifle, then the sort of rail that the scope can attach to. These are some standard airsoft scopes, check your gun rail size first though!
6mm (millimeters)
6mm
:-P