The CSA has to care about a couple things:
1. Be capable of wage war without outside assistance in case of a renewed US war.
2. Maintain slavery.
3. Protect its trade.
So they need to industrialize, a given, cant depend on the US.
Can they really have the luxury of enter foreign wars when you have to concern yourself with possible slave revolts? Maybe if its something limited, Mexico, some Caribbean islands...
They need a strong navy, the CSA lives on foreign trade, the US did not, so there will be the need to not only challenge but to ensure freedom from US interference in case of war. They cant make them, so they need someone else, obviously their biggest trade partner and foremost naval architects at the time. At least for a while, the slavery thing is bound to cause trouble and the CSA would aim to create a domestic industry as well.
Would there be a USN/CSN naval race? If so, that is a sensitive subject for the UK, they would react if it grows enough to be a concern. Plus, there is the Canada border concern, IOTL that was solved to the advantage of the US, here? Doubtful, the US cant push the issue too far, it isnt as big, and the CSA is behind them... is it solved to the UK's advantage or allowed to fester?
In any case, North America is a far more important concern to the UK than IOTL, and its ability to affect outcomes is also enhanced.
Once WW1 begins, the UK would play both sides to its advantage, regulate their trade as far as possible, neither can react too strongly out of concern for the other, they would simply profit as much as they could, but NEITHER would enter the war.
So the Entente folds after the Russian, Italian and French armies collapse in 1917.
Edit: Forgot one bit, the CSA's white population is less than a FOURTH of the US one, do they address that? Allow German immigration (the protestant thing)? Or is it greed too much and plan to just use slaves to exploit the land?