Hi Alvin,
Let me see if I can answer this question for you.
2. Yes, I believed it supports custom entities, however it doesn't support by Microsoft. You have to build the custom integration yourself.
3. Since the adapter is available in US, I don't know when will it be available in other languages.
Have you read this blog? If not, here's the information for the adapter.
Also, if you like to integration GP with CRM, you can look into Scribe. However Scribe is not free.
Hope this helps.
Darren Liu | 刘嘉鸿 | MS CRM MVP | English Blog: http://msdynamicscrm-e.blogspot.com | Chinese Blog: http://liudarren.spaces.live.com