This is fantastic! I can't believe I missed this post!

As to next steps, it depends on where you want to go.
For income, I recommend selling homeless and immigrants for SIM, young citizens and students can be sold or held (but don't forget to pay student debt!)

For growth, the next thing to do is build a second city, in my opinion. This is just because the citizen mining is the most profitable thing to do right now. Keep learning and playing, split your city. I am keeping war tax low, so you could even get away with 1000-1200 popularity cities right now.

Cheers!