Creating a project that for the sake of argument we will call a blog network. A user signs up for an account and then the blog network company creates a subdomain install for the user. For example, userdomain.blognetwork.com.
We have lots of experience with wordpress and zero experience with multisite.
1) By creating admins for each subdomain, what security concerns should we have and how to we address them?
Thank you for all the help.
EDIT: Removed sub questions for better focus