Powershell - Create Sites in IIS 7 - Site / App Pools Credentials

New-Website -Name testsite -ApplicationPool testsite -HostHeader testsite1.test -Id 3 -IPAddress 123.123.123.123 -PhysicalPath C:\Website_Root\WebSite -Port 80

Hi Guys/ Girls, 

I have added the basic site creation for Powershell above. 

I just need to know how i can add the credentials for Username and Password when clicking on Connect As using the UI. 

Also need to know how i can create multiple sites but i can't figure out "$" cmdlet for multiple app pools and setting credentials for a new app pool

Thank you in advance