Here's a rough list of what's needed to make this second wiki a reality. Feel free to add or correct anything listed.
What will be included, besides characters? Real-world collectibles? In-game items/weapons/vehicles/etc.? Films? This will all have an effect on what name would be suitable. While the scope can change over time once the second wiki is running, having a good idea of what will be included will make the initial growing stage much easier.
- OpenID support. The existing extension has minor problems installing on MW 1.13+, and it will need some modification to work with GamerDNA's OpenID server. Ideally, this would be implemented right from the start to avoid any potential problems.
- Semantic MediaWiki. Not a necessity, but it allows for dynamically generated lists to be displayed. I don't know the full extent of what it can do but it seems to have many features comparable to DPL, and Skizzerz says it's not as hard on the server.
- Account sharing. The easiest way to implement this without security issues would be to set up a wiki family and handle accounts centrally, using subdomains for the sites (e.g. en.strategywiki.org and gamepedia.strategywiki.org). The Wikimedia Foundation has worked around this limitation by remotely triggering images that write to the other sites' cookies (or something to that effect), but I don't know how much work that is to implement. Regardless of the implementation, the second wiki will still have its own domain(s) even if they only act as redirects.
- Commons-style media repository. Not only would this allow the second wiki to access the huge archive of existing files, this only has to be done once to allow access from any and all potential future projects (e.g. a Japanese StrategyWiki). This feature works just like on Commons, including the message about the upload being on another site (see this Bulbapedia image for an example). Local media uploading can optionally be disabled, which would probably be best to ensure all images are available to all sites. I don't know about the work needed to move existing images to a repository, but the long-term benefits should far outweigh the effort required.
Anyway, I can't think of anything else at the moment (the proposed change of forum software is a matter that needs its own thread), so there you have it.