Thanks, KOM. I have some success, am able to access a machine on the LAN side of the firewall from the WAN side using the static IP.
My test machine (the workstation on the LAN side, that runs a test web server) is a VirtualBox virtual machine running CentOS 7.6 I installed fresh, for this purpose. It gets its IP from the pfSense DHCP server as 192.168.200.10, which is aliased to one of my available static IPs as you describe. I have ports 80, 443, and 22 forwarded, and they all work.
There is one thing I learned after several hours of beating my head against the wall, which might help any other newbies trying to get this to work...
DON'T FORGET TO TURN OFF THE #%$%$& FIREWALL ON THE LINUX WORKSTATION ON YOUR LAN!!! or the equivalent (Windows firewalls?) on whatever else you're using as a workstation on your LAN. :-(
CentOS 7.6 (and I suspect most Linux distros) installs iptables or firewalld by default, and turns it on with a default set of rules. If you installed it as a workstation rather than a server, the default rules block server stuff. So, all my attempts were getting through the pfSense firewall just fine, only to be blocked by the Linux firewall in the workstation VM on the LAN. I went in there and said "sudo service firewalld stop" and by magic, everything started to work.
Yeah, I know, this should be obvious. It totally got past me. :-(
So for now I think I'm all set, until the next roadblock :-). Thanks for all your help.