Answering the question asked...
Review the WAN FOE sections extensively; (aside: I am not a fan of the LAN/WAN designation In my environment our WAN connections are multiple 10Gbps or 100Gbps connections.) figure out how you want the failover to work. here we use BIND as our dns server and make use of dynamic DNS, OOTB it wants to make use of microsoft DNS.
If these are physical servers you try and make then as identical as you can. the FOE install is effectively a backup of the primary server and a restore onto the secondary server. it will keep your configuration files and logfiles syncronized, but not the database. Let me say this again: the FOE does not do database replication (out of the box).
If you have a single server you might make use of the FOE to configure this, but I have not done it, hence no concrete advice here. I might experiment with replicating the database files, having sqlserver start-up manually, and then configuring FOE to start/stop the process as needed and have Orion talk with 'localhost' as the database server. In my environment we have SQLserver 208R2 enterprise cluster and that replicates independently of Orion.
ask your DBA, or examine the sqlserver statistics to see how much data you have written to the database, and it's size. That will constitute the majority of data replicated between the servers.
Depending on what your purpose for FOE is, it might not be the right product, you might want to look at the EOC instead which might allow you to get one view of the two installs, then if one site goes down it's monitoring goes down with it, unaffecting the other site.