The maximum number of survivors you can have in the game is 10 (including the leader)
You can get 10 of them as soon as you’re able to meet the requirements to fill that blue survivor bar.
some people keep they’re level artificially low by only running auto missions (so they can stay where the raiding is sweet)
By the way you can only raid somebody within 5 levels of your own account
Anyway if you’ve got a question, maybe dig through the FAQ threads before you start a new one, chances are the question you have has already been answered here at some point ;)
Also feel free to ask in the in-game Instant Messaging chat, chances are somebody there will be willing to answer your question