I jumped straight into Crusade after a year break from GC3. The change can be overwhelming but believe me, it's all for the better.
Here are a few basic Crusade tips:
1. Adjacency/tile bonuses are now far more important, especially on buildings that give +integer increases instead of +%.
2. Population is no longer king. Early on, higher population requires a large morale tile investment for a small benefit. Often not worth it until much later in the tech tree. Cities do provide nice adjacency bonuses, though.
3. Resources are king. Get them and get them fast. As many as you can. Asteroid mines are now the best way to get base production on a planet.
5. Invading planets is now a lot less painful and time-consuming but the AI is smarter too.
6. Leader citizens are great for wide empires while focused citizens are better for tall. I specialize in the early game too.