Well with your current setup, you only have 3 options.

Earth, Nature, and Blood.

Take a look at what is availiable and see what you want to go for. You start with a 5 Nature Gem Income.

How reliant are you going to be on your national armies? At what point are you going to have to suppliment your national gold based armies with some sort of magical/summons troops, SC's in order to dominate/survive?

What are the inherent strengths and weaknesses of your nation? What holes are in your armies that can be exploited by your enemies?

Those are questions you should look into as it can mold your nations path, research, expansion and gem use