1), Besides Addons? No. But you can in Earth Special Forces v1.3 which has not been released yet. Check
this thread the links to the addons. Just remember, this forum do not support any Earth Special Forces addons. So advoiding asking questions related to addons on these forums is highly recommeded. Unless you want some evil moderators hunting you. Especially Pain of course.. *runs*
2), Custom Characters, yes. But they only overwrite your current models / characters. You can't add new ones so you can choose more. If you still want to download custom models, such as a Super Saiyan 3 or 4 and you want to overwrite the original old goku, then download the models at
ESF-World
3), No cheats, codes, or what so ever related to it has been added in to this game. Why would you wanting to cheat? If there would be cheats, such as god mode. Server owners would just play lame, no one would ever join the servers then.
4), That's frieza's telekinese. Hold the attack button and you will see rocks flying above you in a few seconds. And releasing the attack button will fire the rocks to where you are aiming at.