Asset Managing for Mobile Devices

Hello. Im currently making a game that has way to many players. Think on a portable World of Tanks or something similar. I have near 300 3D Models that range from 300k to 500k each (FBX) + 100k in its texture. If you do the math, that gives a whoping 180Mb JUST in assets, and im not even adding Maps + Sounds + other Textures or even Text Files. Since the models are diferent from eachother, i have a couple of questions:

• Im ok with the 180Mb + Extras download size, ending in a 300-400Mb game. But if i want to update the game, and add 20 more models, do i have to push the whole game to Android and iOS store do i have to ask my users to download the WHOLE game aggain? How can i implement something that allows them to download JUST the new stuff??

• In game, how the hell do i manage that ammount of assets? I can create a prefab for each, but lets say i need to spawn just 40, how can i keep a list of them?? Right now what im doing is creating managers "The german Manager" "" The Usa Manager" and they have 20 Public variables in a Script, wich i set to the tank Prefabs of each country. Then when the match starts i check a list of the selected tanks, and call the Managers to get the prefabs. This seems to be a clusterf**k and i really dont have a clue on how to organize it better.

Thanks in advance for the replies !