Yes, rails shall automatically place road in the same fashion as the Firaxis editor, perhaps with an option to have different behavior as well. I currently have the "core" overlays (things workers can create that aren't owned by a civ as colonies are) paintable, and am checking that these overlays work equivalently to how they do in Firaxis's editor as a default. Unfortunately not for having more than one building requirement for another building. The scenario format (BIQ) is designed such that only one building can be a prerequisite, and changing that would require a game update. Building requirements for units aren't directly possible, but you can somewhat work around that by having the unit require a resource that isn't available anywhere on the map, and also having it be auto-produced by one or more buildings at set intervals. This works with non-wonder buildings as well, so you could, e.g. have a Tank Factory that produces a Tank every 5 turns until obsolete or sold, perhaps with a higher-than-average maintenance costs or requiring certain goods to be in the city radius if you didn't want to have it kept forever or being placed in every city.