1. I never bothered to think about this, but what are the exact commerce multipliers for each gov't type. It's really hard to determine the optimal without that. (I usually stick to republic, since I can get it fast and wage wars.)
Good choice republic is the best!
2. What is the best settlement point here? Maybe I need two cities? I kinda wanna make ships here. Plus I have an island fetish.
Settle a city on A, D, G, I.
Each city adds to your empire, each city adds to the free unit upkeep limit, each city adds 1 uncorrupted commerce, each city can produce 1 uncorrupted shields that will become 1 gpt with wealth, and each city can support a single specialist.
All together, the 4 cities will produce 4 gpt from wealth, 4 commerce per turn that will either go all to science or all to tax-income, 12 science per turn from scientist (or 8 gpt from tax-man) and under republic, 8 gpt worth of free unit upkeep.
Do not build any city improvements in them, just set them to wealth. One exception, if a strategic resource shows up,
one of those 4 cities should get a harbor cash-rushed.
The island is low priority though, if you have more important things to settle, do those first.
3. Ok, this is probably a no. Is there a way to standardize build orders? Like if I wanted all my cities to build Courthouse-Aqueduct-Library-Marketplace or something? No? Damn....
Maybe, but if you could, would you really want to?
Building improvement X in
every city is the worst strategy around.
Only an improvement in a city at all if it really benefit your empire, and then only build it after you first build things that benefit your empire even more.
Chances are, you'll win the game before completing most improvements that could have been useful.