Hi Krish,
For the Question 1, there are two cases in Central Hub architecture as well. The difference is that in one scenario, the hub system also contains IWBEP component along with IWFND and GW_CORE but in the other scenario, hub system only contains GW_CORE and IWFND but IWBEP is in the backend system. Gateway service can be developed on the system where IWBEP is installed so if your Hub system contains IWBEP, you can also develop the service in gateway system.
The will provide you benefit in case of multiple backend system. If you have to support multiple backend systems for the same service, you just need to have that particular RFC available in other systems and then assign respective multiple system aliases to the same OData service.
Regards,
Ekansh