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The size of your table should easily handle three trains on separate loops. With your trestle set, one loop can be elevated.
There are no 'basic' layouts for three trains that I am aware of - every layout is custom designed to the room and requirements at hand.
I had two trains running on a 5'x8' layout with one loop elevated. A third train was parked on a passing siding that I could switch in.
The two loops were figure eights with the sides connected so that a train could run in a loop, or be reversed using the crossover.
The upper and lower levels were connected with a track on a graduated trestle set, so that a train can go from the top loop to the bottom loop, or the reverse.
Sketch out a plan, then lay out your tracks on the board without connecting them to see if you like it. Continue until you find something you like. That is what I did.

Larry