Possibly going a little too far out of the original scope here, but is this going to be truly free software. By this I mean open source rather than simple freeware.
Considering the way your going to do this, open source sounds like the best overall option. There are several other open source strategy games such as FreeCiv and FreeCol which you may be interested in talking to the teams of, or, if you find it useful, take bits from their code when relevant.
Do bear in mind that if you do this there may be some restrictions. For example, FreeCiv demands that any code derived from it must be released under a specific licence (the GNU General Public License). For details you'll have to read the entire licensing agreement.
It sounds like an ambitious and very interesting product though. Good luck with it![]()
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