When I campained my display layout, it included a three track staging yard and a reverse loop. The layout was 4'x12', the yard was 2'x12.'
We'd run trains through the reverse loop at 15 minutes, then back into the yard after another 15 minutes, then bring out another train. While that one was running, we'd remove the inbound and add a fresh outbound. Each consist was formulated ahead of time.
This was done more for visual variety rather than mechanical reasons, although we'd also have spare locomotives and cars, just in case.
Yeah, it took 16 separate trains for an 8 hour show, but it never got boring!
Rusty