It will be possible to add platforms (parallel to the existing ones) to a station, but only within limits that depend on the station type. For example, a small station cannot have more than three platforms. Bus stops can be upgraded too, e.g. a simple stop can be provided with a turnout/bay.
Adjacent stations/stops can be grouped so that they’re treated as a single station. While this is essentially a hub, the station and terminal are not under one roof, i.e. their original building is retained. Shops and booth can’t be added directly, but the structures will generate revenue automatically as the number of passengers increases.