Black Pudding,
I think your paranoid purely because you worry about things like that. I agree that one has to be careful about social media, that's a factor in everyday life now. But it's something to be aware of with every posting on the internet, if your comfortable with the image and views you portray openly, then what is there to worry about? Believe me, the group interview and personal interview will expose your personality anyway, good or bad.
Of course a bit of caution is prudent, but so is doing everything you can to prepare and I personally believe that being more relaxed before a high pressure situation gives you spare capacity. I'm more relaxed when I know the people I have to work with and I have a vested interest that they succeed as well.
Regarding Doha, having flown with colleagues who were not allowed to have their passports for the duration of their 3 months notice period despite not having their LPC renewed, the impression they gave was that you had to be very careful about what you think and say. One was disciplined for taking his crew water from one aircraft to another during a swap, effectively saving the company a bottle of water. Thankfully, British Airways is a bit more sensible than that!
Please read my comment of 'Don't take life too seriously' and amend to, 'Relax, no-one is trying to catch you out, be yourself, peace and love'