Relatively new to WHM and CPanel, some questions

Hello,

I'm a new user and new to WHM and Cpanel. I just started working at a hosting company that uses it and feel a bit behind.

1) We are using a single server to host approx 16l+ sites, that seems a bit much? If not, what can be done to optimize as the server seems slow at time.

2) I read some documentation on CPHulk, is there a way to get constant updates whenever a concerted brute force attack is happening? What is the best way to prevent a current ongoing attack?

3) Is there an easy way to move sites from one server to another but update all of the references in WHMCS to the new server?

Thanks!