http://dcx.sap.com/index.html#sa160/en/dbadmin/dbserver-s-3165478.html
http://dcx.sap.com/index.html#sa160/en/dbadmin/control-threading-cmdline-running.html
You can find more details about SQL Anywhere threading model in the link above.
It is easy to switch to a higher number of CPUs, if needed. You could also do the opposite, and buy a 2 CPUs license, use one to start with and then go up to 2 when needed (have a look at the second link above please).
About performanace, you should test considering that it sounds like you do not want to dedicate that machine to SQL Anywhere.