I agree, 2 minimum but 3 is better in case something happens to one of them. Chickens are social animals, they really do better with a buddy.
In my opinion this (number of chicks) is more about behaviors. Until my chicks reach a certain level of maturity they tend to form a sub-flock and avoid the adults. If they invade the personal space of more mature chickens (even if the more mature are not adults) they are likely to get pecked. It usually doesn't take long for them to learn to avoid the adults, day and night. They avoid the more mature during the day, they do not roost with the adults on the main roosts at night. Once integrated, they coexist quite peacefully, they just don't get too close.
If you have a lone chick it will probably be lonely and want to spend time with the adults. But if it tries to join them it can get pecked. They are not trying to kill it, they are just telling it to stay away. But they peck hard, it can get hurt. Being a lone chick can be rough. When you are integrating you run into some of the same issues in reverse if you have one older one and several young ones.
Is this always true? Do these things always happen? Of course not, there are always exceptions to anything regarding behaviors. But I'd want to plan on what typically happens instead of hope for an exception.
You still have to go through integration, no matter how many you have. Your plan for that sounds really good to me. I wish you luck with that.
wondering if there would be enough safety in numbers in a flock of 11.
The safety is not in the numbers. It's not like a gang of juvenile thugs are going to avenge an insult from an adult. The safety is that they have a buddy to keep them company so they aren't tempted to try to join the adults out of loneliness.
You also have to consider biosecurity. Where will the chicks come from? They will basically be quarantined in your brooder but I would be a bit slow to bring in any if I did not need to. I think if two hatch I'd stay with two but if only one hatches bring in two more.