Paying for tribe land is a good idea, with resources or tokens or anything.

I wouldn't even connect tribe area size to the member count. Let a tribe to upgrade their totem and have more land if they can pay the price and able to maintain it. This way smaller but very active tribes could own a big area, while tribes filled with inactive accounts would shrink.

A homestead totem should be free or require very small amount of stuffs ( like 5 grass or something) to help new players to adapt to the game. Otherwise they would be in a serious disadvantage and that may drive them away from the game.

The higher level the totem is the next upgrade should cost more and more.