There is no way to know how many people will be in my group on Z-Day which makes it very hard to plan teams. I came up with this formula (May not be the very accurate but it will give me a general idea of how many people MAY be in my group.)
First I add up all the people that live within walking distance that will come. That number adds up to 16.
Next, I add the people that I called that are coming. That number adds up to 12.
That adds up to 16+12=28. We could either round that too 30 or 35 to be safe. So I now have a general idea that 30 to 35 people will be in my group.

A Team:
The A team is the team that sweeps the store in Phase 2a:Sweep and Clear. This team needs to be strong, as they will mostly use Hand to Hand combat and needs to have a lot of members to be able to effectively clear the stores. For this group I chose 12 people.

B Team:
The B Team is the team that immediately tries to lower the shutters in Phase 2a:Sweep and Clear. This team doesn't need many members, as there are only shutters on the main entrances and windows. I chose a team of 5 for this.

C Team:
The C Team is the team that hotwire cars and park them infront of doors and windows in Phase 2a:Sweep and Clear. This team will need a good amount of numbers due to sound. When we begin starting all these cars, it is going to alert any infected nearby. We need to get it done as quick as possible. I chose 10 people for this team.

D Team:
The D Team is the team that will cover C Team while they are busy hotwiring cars in Phase 2a:Sweep and Clear. They will deal with any infected that are attracted by the sound and will help C Team in any way possible. For this team I only chose 5 people. I don't plan on them being out there long enough for many infected to come fight them.

X Team:
The X Team is for anyone who cannot function in any other team. This may be due to a disability or anything of that nature. I plotted for 3 people to be in this group. If there are no people that can't perform, then we will forget about X Team but I planned for them just incase.

So in the end the teams look like this:
A=12
B=5
C=10
D=5
X=3
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35