You will not have to bother about such issues unless you're assigned a static IP address by your ISP (common for corporate connections)
Even then, you will be protected by your router's firewall as well as your machine's personal firewall.
Most ISPs provide dynamic IP to end user devices, which are auto-renewed after a fixed time of lease. Whomever portscanning your IP from outside is stopped at router (if it has a firewall or IPS)
NAT will as help in preventing unnecessary traffic from reaching your personal device.
Inorder to know the IP lease and mapping and customer data, attackers must compromise ISP itself, which is not an easy task.
Changing IP address via VPN or Proxy won't change the ISP assigned public IP, but hides it.
Another way of anonymity is to use TOR browser package.
Edited by Nikhil_CV, 31 May 2015 - 09:53 PM.