<<
How many simultaneous connections are you expecting? that's the big
question we are looking at a range of 1400 - 13000 orders per hour

>>

This does not look like much of a challenge - but I don't know the
nature of your orders processing!
Checking your SQL could be a good thing - I'm thinking of indexes.

<<
What page cache number and page size have you tested with? page
buffers: 2048; page size: 4096

>>

If you are using SuperServer: You are using about 8MB (out of your
4GB RAM) if there is just one database. Increase the 2K page buffers
to 8K (or maybe even more). The 4KB page size may be ok, but test
with 8KB as well. Maybe you could benefit from even higher numbers.
If you are using ClassicServer you will have to think about number of
users (each with their own cache).

And, think twice before turning ForcedWrites OFF.


--
Aage J.