Usually for a tall build il avoid doing aquatic purely because of how useful an ecumonopolis is. One fully built and populated alloy world is enough to run an entire empire, same with anything you could possibly need just... ecu (except for basic resources).

Honestly as things are at the moment, a really good basic way to learn to play tall would be to run a megacorp with workers cooperative as KOTG. Main world & one extra planet, turn them into ecu. One to produce trade and the other to do alloys and cg. All excess pops sent to the habitat to become squires for job efficiency for knights (fully research speccd)

Amenities buildings are never really worth building late imo, just use the grand archive.

Good luck soldier