Hi Katie. Kurt isn't on much these days. He stops in from time to time, but I'll answer for you.

Red eyes are social and tend to prefer others. Too many males in one tank and there may be some leaf shaking, but generally if it's not too crowded, they should be fine.

Depending on the size of your tank, you can house one per 10 gallons of space.

If you purchase them together you can quarantine them together. If not, you should quarantine them separately to prevent any risk of disease or contamination.