The earth station should be as simple as possible, while providing the following services.
Flights delivering to the station can gather up waste and return it to Earth. This includes waste from the station, and refurbished and upgraded equipment. Equipment can be returned to Earth for refurbishment.
The configuration of the station obviously requires careful study. The station must be able to dock a variety of vehicles and equipment, and the overall configuration varies. Some equipment temporarily near the station can be free flying, although safety considerations might cause mechanical restraints to be preferred. Expandability should be taken into consideration.
Unnecessary luxuries should be avoided. One example is artificial gravity. While this is possible, it vastly complicates the station and has marginal utility. With two month tours, its benefit to crew condition is negligible. Artificial gravity might have scientific uses, but this topic should be ignored for now. Similar considerations apply to a hydroponic garden.
A plausible configuration consists of a 20 by 50 by 100 foot box. At the center of the box are two pressurized "tanks", cylinders about 12 feet in diameter and 25 feet long, with thick steel walls and hemispherical ends. These are connected to a "vertical" cylinder at the center, which has a double airlock to each cylinder. Entry to the vertical cylinder can be from ports at various locations on the box.
One of the cylinders is the quarters, for a crew of 4 or 5, with "cots" for crew temporarily in residence, for example for lunar travel. The other cylinder is the work area, which has operating consoles and R&D stations.
One of the 50 by 100 foot faces is for docking Earth launched vehicles. The other contains docks for various manned and unmanned Earth orbit vehicles, and lunar travel. The latter includes storage of lunar vehicles. The 20 by 100 foot faces have 4 large power modules attached by "constraint boxes", so they can rotate; electrical connection might be by wipers or microwave. The remaining faces are roots of "booms" for constraint boxes for various equipment in transit or "home" position.
The total weight of the configuration varies, but a nominal weight of 100 tons seems within reason.