Adriana,
I don't work on the new Mixed Fleet but can answer some of your questions. I work on Eurofleet.
You get your basic pay during training.
Accommodation is not provided.
After their interviews some people hear straight away and some wait ages and it does not seem to make a difference if it is a yes or no, it seems to depend how busy BA recruitment is.
Some people get courses straight away and some wait ages again no reason why!
People who have to get foreign criminal records checks usually get given more time before their training course starts as the criminal records checks take longer.
BA take all people that have a right to work in the EU, nationality is not at all important except obviously you need to speak good English. Personality and the ability to show you put customer satisfaction first in every thing you do is the most important part of the interview process.
I have pm'd you with the name of a blog that has other new crew posting on and if you get in you will be able to find people on your course to share with.
Hope that is a help to you.