Setting up a second Google Voice account on your OBi follows the same procedure as setting up the first account, except that you click on SP2 on your OBiTALK dashboard, instead of SP1, which I assume is already set up with the first account. Before you do this, log out of GV account #1, and log into GV account #2, in the same web browser, then click Ctrl-T to open up a new browser tab and perform the OBiTALK/GV setup. You'll see a pop-up dialog box. Make sure that the Gmail address displayed shows the correct Gmail account that is associated with your desired GV number.
As for using a second phone, you'd either need to buy another OBi 200, or replace your existing one with a OBi 202, which has two physical telephone line jacks. If you configure both GV accounts on the one OBi 202, then both GV accounts will ring the same phone(s) plugged into the one telephone jack on that OBi. The SP2 account will have a "distinctive" ring (a stuttered ring) so you can tell them apart.