Are these ACS keyed ignition switch and lock sets FAA Approved?
Yes, they are STC'd.
Is the faceplate With start (P/N 11-03667) included in A-510-2K kit?
Per the supplier: Yes, the faceplate is included.
Is this STC'd for the Cessna 150 and 172 as well? Is the STC Copy available?
Yes, this is STC'd for the C-150 and C-172. Please review the STC pdf which is located in the "Documents" tab of the web page to verify your serial number is covered.