I was Challenged
capx
I used 3 layouts here, and you can use the platformer to walk either left or right in a loop of layouts.
The doors are close to the edge, it would just require some smart level designing to make it look better, some things from the beginning of the level would need to be on the end of another level. If you make everything relative to the doors with positioning, you are likely to get away with a short blink or flash in the screen.
As for enemies and objects following you at a distance ... that just takes some smart procedural approach.
All in all, the mulit layout transition, smooth, is something which is likely not the intended working of levels and layouts ...
In some of my games I simply use a fade out to black, load other layout which starts out with a black layer, and fade the black away again.
For what your desiring to work, I would design really big levels, like 10k , 10k, which would not need transitioning.