One suggestion, if its a small environment, sometimes a high end PC will do the trick until you get the budget in line. Normally the features of a blackberry attract more and more people to want them then you get the new server for the BPS. Or better yet get a server and go virtual with VMware and use it for more than BPS.
As for the the OWA setup here is a quick set of instructions:
http://www.blackberrycool.com/2005/05/how-to-receive-email-on-your-blackberry-from-outlook-web-access-account/As for the sent items, if you are using OWA they will show up in Outlook sent item folder.
For the delete, most people want it deleted in both places! With BIS version 2.3 it is now possible for it to delete both places. But to answer your question, for the delete only to happen on the bb device, you need to configure that on the device, go to Messages > Options > Email Reconciliation, then select only Handheld as option.