I'd be happy to work on a smelting array. I can design the building and include space for smoker, blast furnace, and regular furnace super smelters as well as areas for individual furnace use. I'd work on the design on my creative world and solicit feedback in this community throughout the week, and then I'll just have to get the materials and copy it over.
Putting it right next to the mine could make sense. Personally I think we should build it near the bamboo farm. The bamboo can be pumped directly into the furnaces as fuel without having to craft anything. There is also a lot of empty space there so we could build a giant horizontal bamboo farm afterwards (as opposed to the space-efficient but low throughput vertical farm we have). This will require honey or slime blocks for collection. Excess bamboo can be used as building material when we update to 1.20.
As for public transit... The streetcar is cute, but to be frank its utility is quite low. The loop design runs into issues whenever one cart ends up going the wrong way. To make matters worse, the speed of a minecart depends on whether or not its empty. Even if all carts are going in the same direction, it is inevitable for them to bump into each other. What we really need are automated stations that deploy and remove carts from the system when not being used (and maybe double track). However, these take up a bit of space which we don't have in the center city. Since the streets are quite narrow, we'll need a subway.
That said, the city is really compact right now and will be for a while so there's not much point in having a metro. And we also don't have that much infrastructure outside of city limits, so regional rail should be low priority as well.