When setting up a MN, there are 2 wallets involved, each on their own device. The MN Host wallet, which is running 24x7 and the MN Controller wallet, which can be turned off as desired, and it contains the 10K PIV collateral.
Your MN Host needs a unique WAN IP address. This can be the IP address your ISP provides to you, but they are typically DHCP, which means when your router reboots, you might get a different IP address. If that happens, you will need to update your MN setup, issue the START command again, and wait 3 to 5 days to get back into the payment queue.
When you get a 2nd Masternode, this method typically won't work, because your ISP only gives you one IP address. This is why many people use a service like AllNodes to run their Masternode Host for them.
You can run them using Tor, to get unique IP (Tor) addresses that way though. But, that is much more technical.
Hope this helps!