If it is for the internal hosts to access the Internet, you should use "Hide" NAT for each network object and specify "Hide behind gateway's address).
If you want to be able to reach some hosts inside your network from the internet, you'll have to use port redirect from your DNS service provider for public host in each network (i.e. if you have four Web Servers, you'l have to create HTTP Redirection Records pointing to https://yourpublicip:fakeport#), implement manual NAT rules performing PAT and configure Manual Proxy ARP.