I had on idea about houses. each player (no level limit) can have a house, in this house you can have a lot things:

1) the house - you can have the house and you can build it as you wish, you can put in it furniture like tables, chairs, sofas, television, Etc....
2) the garden/+river - you can have your own garden and you can have a river in it, you can furniture the garden too, and you can plant a vagatables/fruits/flowers/trees/brushes/Etc wich you can use later for recipes/trading for other things (for example: you can make from is food for the pet system, or you can trade those things for the pets eggs ) or you can use it as missions/etc matarials.
you can get the seeds for the plants from special shop, the shop dont have to be in gols, it can be in matarials (for example: 50 Fairy's Powder = 1 cherry seed).
you can raise the seed by geting the water from the river or farm the mats wich help the seed raise from mobs.
Plus you can have a little farm where you can keep animals like chickens, cows, etc thats gives you eggs, milk, etc and you can use those mats for recipes/for getting a special seeds.

You can invite your friends to your house, you can have partys, you can do whatever you want in your house becouse its your house


~thats all i can write so far, if you have question you can write it in the comments and ill answer it ^^ ~
~sorry about my bad english x3 ~
~i gave my idea about this pet system but you can change it as you wish :3 ~
~the House System and the Pet System can be connected if you wish, but they can be not connected, its up to the GMs ^^ ~