[PvK]

Range 20 on a starliner is fairly limited, but not useless (also considering the cost and that IIRC you may have no other way to build a ship that can haul a population unit at the point that you can build those starliners) - you'd just need to provide supplies for where you want to use it, which is also an intentional part of Proportions - you're supposed to have logistical problems to solve, and using tankers is a useful option (building cheap ships with a lot of supplies and fleeting them with ships that don't have much range themselves).

I don't expect the AI can build good starliners except by accident, though it should be possible to fiddle with the AI to get it to do so. What I'm thinking of doing is resorting to some AI racial techs to provide a challenging opponent rather than investing the time to get the AI to play by the rules designed for humans.

The number of AI empires isn't limited by the definition of a high number of AI opponents for randomly generated games. Also there's no reason the player can't change that setting if they want a full set of AI opponents. But, ya, I might as well turn up the number on that default setting.

The construction minister, when on, decides which things to build without your orders. The transport minister decides whether to order some ships to move units and population around or not.