Okay, correction, I do use women to farm, but I get most food by hunting and trading.

you combined that with the road ability mentioned before, and that can make some different type of scenarios, were controlling a trade route, building the road for it, are key to get the resource and build your wonder for example.

It will be difficult for you to sell the idea that way. The issue of balance always hinders innovation.

one element that might be fun would be market routes at the exit of maps.  Something that you cannot control, but a point for your merchant, or merchant ship to reach. It is only interesting if the gain in term of resource are important compare to what's available on the map.   All the players could send merchant to it all the time, the trick would be to protect the trade route

I agree with this, but Spartans already have infantry swordsmen (Skiritae) and... Siege ballistae aren't Mercenaries, they're machines that don't have ranks. I don't think you should be able to recruit anything other than Rams from captured Arsenals.

This is kind of already the case with certain civs/buildings, like the carth mercs. However, I think it should be made consistent unless there's some huge balance issue (like multiple discounts leading to 10 metal mercs).