From a memory management standpoint, different tilesets are what layouts are designed for. If you use different layouts, you won't have to keep all the currently unused textures in memory. You'll then be able to load a lot more/bigger/nicer textures per any given layout.
Note you can use the same event sheet for all of your layouts, while season specific events can check a simple variable that keeps track of the season as a condition.
Multiplying the layouts by 4 doesn't seem like much additional work to me, considering you want different seasons to begin with and I'm assuming you don't want the seasons to look the same. That means the 4 sets of different graphical assets have to be made anyway, which is the bulk of the work.
As for setting up the map 4 times, I believe you can just copy and paste the painted tilemap object and just change the tilemap source image, assuming your 4 season source images use the same tile layout. You'd probably want to use a program like Tiled to build those maps. As an advantage, having them separate allows for individual changes to the map itself for each of the seasons as well.