There is a lot of breaking changes between SMP 2.3 and 3.0. You can still use a MBO model developped for 2.3 and run it on a 3.0 server instance.
The only way to take advantage of OData in SMP 3.0 is to reimplement all the data logic using the OData API.
I'm not sure if the Offline OData works as it should in SMP 3.0, we ran into complicated issue in couple projects in the past in regards to this.