Hi!
I’m kind of fumbling with something similar, but the first thing you need to decide is your density of vertices or height points.
DEM files have a certain resolution; One height value per, usually 10 or 25 meters for the free data. Sometimes 1m or lower.
Unreal terrains at 100% size (default) will assume each height point is 100 Unreal units (cm) apart, so your 4097 map would be roughly 4km in 100% size. To get it 50km you’d have to size it up over ten times, but it would still only have the 4097 pixels so the terrain will be very rough.
If you want 50 x 50 km of 1m resolution data you will have to tile your map as the max height map size is around 8000.