The biggest caveat with any casual free-to-play game is the premium currency system. Just about everything is on some kind of timer, and as you progress, those timers get longer. Don’t cave and spend your precious gems on speeding up production - save them for something important that you get to keep. Make a point to complete missions and clear natural obstacles to build your gem count. Maybe it’s a building that’s only available for a limited time. Maybe it’s your next builder’s hut. The point is, you need to save the gems you earn from missions and terrain clearing for stuff that’s more than just a convenience. You shouldn’t even spend the gems they suggest you do during the beginning tutorial session.
When you do have enough gems, think long and hard about what’s important to you in the game, since if you want to get through this without paying dime, it’ll take awhile before you make another major purchase. On the flip side, you’ll have a hard time getting through the competitive end-game content without spending some cash.