I'm Hannah Erlebach, a Cambridge maths graduate, and I run the Cambridge AI Safety Hub (cambridgeaisafety.org) alongside supporting EA Cambridge.
In response to the first two questions:
Will check with the other organisers and get back to you on the third question.
Hey, that's a good question - if you're really struggling, you can form a joint team with another uni group, as long as you have at least 5 team members between you. In this case, prize money would be split 50/50 between the university groups.
In addition, as long as some members of your team are members of the EA uni group you're entering for, you're welcome to recruit other friends in order to get to 5 team members.