Depedning on size, the maximum allowable map size in 2x2 configuration is probably what you have to use to maintain things working.
However, if you are serious about your project and wanting it to work, you will probably forget entierly about landscapes and map sizes and move on to better systems of your own making, or possibly of someone elses making that isnt Epic.
There is plenty of work out there that supports infinte maps created at runtime, just nothing made by epic.
I guess, unless you count stacking up infinite amount of rock instances, turning on nanite, and calling that a “solution”…
Anyway, point being. What you are doing is already going to fail just because you want to know about landscapes.