I have attached a generic diagram of what these sites look like now. My intent is to optimize the replication based on cutting down unnecessary traffic and setting up site-links/costs based on WAN links. As you will see some of these settings were customized, and without much (or any) documentation I am trying to analyze "why" and make changes accordingly.
As you can see some servers were set as bridgeheads and that is a concern, esp as the MainSite. From what I know this puts all the "replication eggs" in one basket for this site and that probably isn't good. I am thinking of setting at least 1 or two more DCs here to be bridgeheads. I'm not sure any of the other sites need their servers set to bridgeheads as they all have single DCs.
There are site links for: Site4 to MainSite (includes all sites but Site2), Site4 to Site3 (includes all but Site2), Site5 to Site4 (all but Site2), Mainsite to Site4 (all but Site2), MainSite to Site6 (all sites), MainSite to Site5 (all but Site2), Mainsite to Site3 (all but Site2). All these links use the default 100/15 cost/repl interval with the exception of "MainSite to Site6" which uses 120/180. This does have the slowest WAN link and is geographically the furthest. "Bridge all site links" is enabled but I would like to disable this and potentially set this up manually.
Based on this info, how would you go about optimizing these site links/bridging as well well as bridgehead placement? Should we go with making 2 more DCs bridgeheads at "Mainsite", maybe bring up another DC at DRsite and have Site2-6 replicate with only that and MainSite only with DRsite? Thoughts?