You could always just use the rules for diagonals on page 252 of the DMG
I think that's plausible, but the boardgame and the video game are very different. If the video game is descended from the board game the change of medium made some big changes. The board game has a big emphasis on trading that the video game cannot reproduce. And the board game doesn't have individual city management.
I haven't been on there in a long time but the link below has a way to play it online. http://civ.rol-play.com
And if you take 3 levels of armorer you can have your armor change to fit your new form to have a good AC and shoot lightning as you slither around as a robosnake
I have tried doing XP triggers before and I found it a little difficult to keep it fair between characters. If I were to do it again I would award the whole party XP when an individual fulfills a trigger.