How to configure FlowWright multi-tenant sites exposed publicly to the internet?  

You can set the public DNS to any URL you want; you will have to change the URL within the FlowWright configuration settings to the new URL and also the FlowWright multi-tenant URLs. Use ports 80 or 443 for https traffic.

Given that we would have multiple tenants under one server, would we need to implement a DNS entry per tenant so that each URL is uniquely different? What IIS changes (if any) do we need?  

You need 1 DNS entry, for example, *.yourdomain.com. If you tend to use SSL, you will need a wild card certificate for *.yourdomain.com. You may also configure IIS to be *.yourdomain.com

What would you recommend if we had multiple servers with multiple tenants per server?  If we had a wildcard, would we need a different domain per server?

You don’t need a domain per tenant, only the parent domain is required so that you can do something like this

*.fw.forwardadvantage.com

each tenant will have the following: then

tenant1.fw.forwardadvantage.com

tenant2.fw.forwardadvantage.com

you only need to configure *.fw.forwardadvantage.com