Thank you for writing.
I am getting straight to your questions:
1) Please refer to our online documentation
for information regarding synchronizing RadGridView with OpenAccess. The OpenAccess infrastructure implements IBindingList interface and this allows automatic synchronization for any CRUD operations between RadGridView control and its DataSource.
2) Yes, it is possible. You can implement new custom row using the codebase of our Custom Filter Row example in our Winforms Demo Application. The example is located in RadGridView section > Filtering > Custom Filter Row
3) You always have access to mapped domain class object using DataBoundItem property of GridViewRowInfo.
I hope this information is useful. Let me know if you need further assistance.
the Telerik team