The other way to get more gems is simply to do the temple or pit of doom trick. Which one you do depends on whether you play the game on a computer, a tablet or a cell phone. If it’s a tablet or mobile, you get the temple of doom. Otherwise, you get the pit of doom. Either way, you can earn unlimited gems.
First thing to do is to find a way to kill all of the Astari. You can do this with multiple meteor strikes, fingers of God, or other strategies, but the best way to do this is to build swamps in their territory, to the upper right side of the Astari Temple, so that during the festival season, they all walk into them and drown. Once they all die, they will never come back.
Now that you’ve done that, send followers into the pit or temple, preferably from your small houses and not from your settlements. Each follower that you sacrifice will earn you a gem (or diamond), making this easily the fastest way to earn gems. It’s slightly expensive as far as belief goes but it’s fast.
If you want to really guarantee that your settlement takes up as little space as possible, build your first one and then surround it with trees. Merging new abodes with it or building new abodes on top of it will then cause it to grow taller, but not wider due to the trees blocking it, but the trees are small enough that you can build a ton of abodes around it for absorption purposes. Keep other abodes on the outside of the immediate area so that you can summon builders for free (unless it’s a builder settlement).
If you reset the game and start a new game, wait as long as humanly possible before you construct a farm or a mine. Build the settlement, just don’t let your farmers and miners build farms and mines. That way you will literally never have to spend any wheat or ore when you decide to build a new abode.