hmmmm, these things bother me.

This order matching engine will be strictly single-threaded and purposeful.

bitshares is not of such that you can use any single-threaded thinking or implementation. Yes, your implementation should probably run in a single thread, it just has to iterate over the order books. However, your implementation will run in several places at several times.

It is hoped that the input will be clean and optimized (which could be offloaded) to improve throughput.

You can never count on clean inputs.
Thus you will clean and optimize inputs before handing it to your process.
If you build two modules, someone later can come and place something in between... thus you can never count on clean inputs.