To get something close to a Status Quo Ante Bellum, including colonies, I'd expect that German boots will still be on French soil, thus giving Germany something to offer back in exchange for some colonies returned.
I agree that Japan would be very unwilling to return the colonies they took without a very good reason. The USA leaning towards getting into the war on the side of the Central Powers might be enough, especially if said belligerence was seen by Japan as an excuse for the USA to grab pieces of the Pacific. Germany could say, "We want it back, or we aren't ready to talk, and the USA is looking at taking those islands. Will they stop once they get there?"
As Germany, I'd want to keep the 15" gun ships, the Mackensens, the 12" gun battlecruisers, and perhaps the Konig class. The Kaisers and the 11" battlecruisers are salable, or perhaps the 11" battlecruisers would be suitable for conversion to experimental fast carriers. They're fast enough to keep up with the fleet, and mostly useless as combat ships. If the Ersatz Yorks are far enough along, complete them, or perhaps build one of them as a carrier instead of an older battlecruiser--but only if the ship isn't too far along, and the Reischstag doesn't want to pay to complete them as Large Cruisers.
Continue to work on the guns for the L20 Alpha, but don't lay the ships down. Instead, learn from the war experience, and only then, lay down some new hulls. There's no need to build an expeditionary fleet, Germany's vital interests are in Europe.
I suggest keeping the Konigs to show the flag in foreign stations.
Light units--a few decent cruisers for freign stations and showing the flag. If raiding is a plan, make sure that they can use captured fuel, which, in 1920, recommends against diesel.
Just some random thoughts there
