Yes Alex, that's pretty much it.
It is necessary to add the IP address as an alias on the interface screen and create a network object to be used in the rule. If I encounter any issues with my customers it is that they have created the network objects (so the rule looks OK) but forget to add the alias address on the interface.
Another potential scenario is if you have (lets say) 5 public IPs and 5 web servers on your internal LAN. You can create 5 individual rules, but you can also make use of the Netmap object. You define your IP address objects for the respective internal and external IP addresses and then create a Netmap object (mapping external addresses to their corresponding internal redirects). Though I haven't done this myself for a while, I beieve you then use this Netmap object as the destination value in the rule and it will then automatically use the mapping in place of the redirect host value. This consolidates the 5 rules you would have previously created into a single rule.