This is not actually true. NAT rewrites the apparent source address of outbound connections, which has no impact on inbound connections -- any inbound connectio

This is not actually true. NAT rewrites the apparent source address of outbound connections, which has no impact on inbound connections -- any inbound connection that worked before you started NATing your outbound connections will continue to work after you start doing so. You need a firewall for security, and NAT doesn't do anything in that regard other than make it harder to understand what's going on.