1. No ongoing cost for the hardware device you bought.
2. Why would the sale not come under the applicable laws applicable in your jurisdiction?
3. The OBi devices support SIP and the XMPP interface to GV. There were concerns that Google would withdraw XMPP in May 2014 but that has not happened. Currently there is no reliable information one way or the other. I have no knowledge of MagicJack.
4. The OBi200 can connect 1 phone instrument* and up to 4 ITSP accounts. Additionally another 8 Voice Gateways can be used for making outgoing calls with SIP ITSPs who do not require SIP registration. Subject to your internet connection having sufficient bit rate, you can have a calls on the handset and another one handled by the auto-attendant. You can also have 3-way calls. (The mixing is performed in the OBi, not by the ITSP.)
The Obi202 has provision for two phones and can handle two simultaneous calls on the phones and a third by the AA.
5. On the 200 all incoming calls go to the phone. On the 202 you can freely configure how incoming calls from each ITSP account are routed. To either phone or to both.
6. You can configure dialling plans so that calls are made via a certain ITSP account according to the dialled number. Additionally you can over-ride that by prepending **n (where n is typically 1 to 4) to a dialled number. For the 202 all of that can be set independently for each phone.
7. Yes.
http://www.obihai.com/docs/OBi200DS.pdf8. OBis usually come with a 110-240 volt PSU.
9. No built-in proxy.
10. 1-way (and 0-way) audio is sometimes encountered but is usually solved by tweaks to your router's config. However YMMV. The Obis are no worse than any other ATA in that respect.
Unless the few dollars difference in cost is crucial or you are certain that you will never want the second phone capability, I would recommend the 202 over the 200.
(* To clarify, each phone jack on an Obi will support multiple phones - wired or cordless - but they simply function as extensions.)