second Ip for Securiy sidecar

Question on second IP address I currently have two  10.X IP addresses one for my Internet connection and one for the Home Security Side car,,,I am going to update my cable modem from the one provided by comcast,,,

Q1 Will I be able to keep the two 10x IP addx currently assigned?

Q2 Can the two routers be Connected to a single port Cable modem via a 1Gb switch?

Q3 0r will a cable modem with to WAN ports be required?