The questions that you raise are good ones.

Who would be responsible for the defence of independent Catalonia? Could they be financially independent?

Also, as a general question, is the current tendency of regions wanting independence from the larger state of which they are currently a part a good thing?

Scotland from the UK, the UK from the EU, various central European countries have been split into smaller units. Surely this makes them a lot more vulnerable to potential aggressors?
We all know that the UN and NATO for all their good intentions, are pretty toothless in the face of actual aggression.

Maybe its because the present generation has never experienced something like World War two and don't appreciate just how easily things can go wrong.

It seems to me that we are exposing ourselves in a very dangerous way.