I like your field, looks nice.
Are you spawning above the landscape and falling through or actually spawning below the landscape?
The obvious question would be are all of your spawn points above the terrain.
If you can pinpoint where you are spawning find that point in the editor and see if you have a spawn point in that location.
Also check if the point is at 0,0,0. If so, you likely didn’t configure your spawn points or world settings correctly.
As for speeding things up, for vegetation try making one vegetation template that has all the correct settings and what you want, then you can copy that into the vegetation layers for your individual levels, that way you don’t have to go through and set up each foliage on each level. That would be a nightmare.