Based on the threads you referenced, here is my shopping list - am I missing anything?
The SEM and the IQ Panel 4 are mutually exclusive.
You would either reuse the existing Vista system and 6160 keypads with the SEM-300, OR replace the existing system with the IQ Panel 4 and Hardwire translator, just reusing sensors. 6160 keypads cannot be used with the IQ Panel 4. Use an IQR-PG (the new IQ Remote keypad) for additional keypad locations.
Either way cameras would not be compatible.