The answer really depends on the lab vendor. If they can accept all different type of messages on one thread, and if they will send all message types on one outbound thread, you’re fine. Whether orders get routed to the reference lab or to one of the foreign labs, cloverleaf can handle that routing.
One thing to consider {a.k.a. “my two cents”} in having a limited number of threads in/out of the lab system is message volume. If you have several sending systems, sending multiple message types, the message volume may be such that it is advantageous to have more threads for load distribution.