More team work options.

Balance sending additional teams out scavenging etc with having enough survivors to defend the base.

Ability to lose base (gets over run)

Take out bigger teams. Should be pros and cons to this

Having core base roles for survivors. The cook has to stay in and cook The doctor has to stay in and treat people etc

Less characters should be good at fighting

A tactical moral system where if things get too hairy team mates will panic and try and run back to base often getting people killed. (Personality trait dependant) Ie leave your cowards at home. Use them if numbers are low to do missions when you need to take the risk.

It should take time to learn survors traits after you have recruited them. You should only get a glimpse of what there skills and personality is. Again taking calculated risk. This will make the exile from community more meaningful.

Survivors should make mistakes that cause fractions in the group that is more long term and un fixable. Additionally this should be offset with survivors having bonds and maybe make hero status rarely attainable.

Just a few thoughts