Looking good so far. Do you create them natively at Civ3 resolutions, or at a larger resolution and then scale them down? Civ3 resolution will work, of course, for Civ3 as well, but one of the benefits of having a new engine is we could put higher-resolution graphics in the game as well. Puppeteer believes this may be as straightforward as adding them, and then you simply get more detail when you zoom in.
These are rendered in civ3 resolution. While it is a good idea to include zoom-in, you should consider that unless many new gfx are made (thinking primarily of units) in larger resolution, it will look rather strange when zoomed-in.
While I could create these with more details (eg 200% the current size), the issue is about how viable it is to expect enough new gfx to fill everything when zoomed in.
My suspicion is that if the plan is to use all-new gfx for everything (so that they can be zoomed in and look great), this will certainly require some sort of crowdfunding to pay the artists since it is a lot of work.
Otherwise, an idea is to just zoom-in current resolution. I think this is a 200% of my French medieval metropolis:
And this is the Byzantine metropolis, in an actual Civ3 mod zoomed-in to 200%:
(land terrain is by Vuldacon)
While creating 200% size new map gfx is doable, I am not sure if it is so for units (since there are so many more of those...)