Unable to level without using coins

You could go all the way to lvl 20(highest lvl) without spending anything, but it would be very hard. To get treasures, sell resources, hunt a lot, capture some forts, make sure to collect daily gifts, just save your money up. You can get pretty much anywhere in this game with patience and hard work

I didn't buy coins until I was late into my level 12 rank, and that was to buy all level 15 gear. Yes, it takes a lot of patience but use the advice given in this thread to help. Raiding forts is a great way to get extra resources and sell what you don't need, it will get you more money than occupying a fort.

lvl 17 and spent way much more then a dime XD

I can't believe how lucky I am! I still haven't bought the nugget to level up yet but today, I received a daily gift of a chest of level 2. After opening it, I've got a level 0 nugget! So people do get treasure of this type depending on luck. I have a ring of level 8 fortune and my fortune is 26 x 8.

This saves me 30000 so I can use that money to do tech research.