Look for inherent knowledge creating experts(leaders)
A potential leader is someone who is a bottleneck. an expert. They can become a leader by coaching and sharing on that knowledge. Architects are a good example.
If you get to choose the people who will be in your team, I would look for people who are leaders in specific fields, but that are willing to teach and share their knowledge.
These are the people that will make sure they are not the only expert on technology X in your team.
Look for people who like to speak publicly
They make great teachers, and are great at sharing knowledge.
Look for people who work well together
If people already have fun working together, everyone benefits.
Look for people willing to sit with everyone else
If you can get the whole tea in the same room easily, communication wins.
Look for people that COULD make you feel stupid if they wanted to, but make you feel great to be around them instead.
There aren’t many of those, but people skills are the wheels that drive a good team. Knowledge is the oil.
Look for people with time
If they start out not having time to learn (survival mode), you are already starting a race with the odds against the team. I would rather have a person with potential that is not doing any other projects currently, than a person with the realized potential, that is doing two other projects at the same time.
The idea is not to create the perfect team, but to create the perfect soup mix. Get ingredients that grow and assemble as they come close to each other, that with the right mix of love and care, can grow to be bigger than the parts.
If you build a team, build a team that has the best potential to grow leaders within in the future, because you won’t find the perfect team today.