Use the same BESAdmin account for both BES and Exchange Servers, just assign the permissions on the Exchange 2007 machine first.
The install your test BES, don't worry so much about policies. As long as Activations, email and wireless sync works you are golden.
The second option is the best one, just upgrade the CDO/MAPI components and upgrade to 4.1.5 on your production BES.
Then you are good to go.
Feel free to ask any questions.