It's ok to use address 2 for the OVR. Each type of device has its own address range, and the addresses don't conflict with each other across types.
Keypads are type 1, zone input expanders are type 2, output expanders are type 3. So if you choose to add a wireless adapter at a later time, no problem assigning it address 2, even if you have an output expander that also is assigned address 2.