The criminal mastermind is the next challenge I would like to do. That is going to be a tough one. Would really hate to be the one to die first.
Loyalty challenge I haven't done either, so would definitely be up for that as well. But doing the criminal mastermind together would complete that challenge anyway, so that saves time.
I'm free every day at the moment from Monday until Thursday for a few weeks. I work all day Saturday until 8pm, Sunday's until 9pm so those days are awkward if we were to do every heist in one go as it's going to take 6+ hours to do.
As long as I know a time I would definitely do my best to be there.