Hi Vishal,
I want to make one think very clear, SMP 3.0 has SAP integration Gateway component meaning you actually DO NOT need a separate Gateway installation. You can expose your OData service from your ERP system to SMP 3.0 through integration Gateway component, they have made it very powerful.
Having said that, if you/architecture are/is already aware of this fact and for some reason architecture team still wants a separate SAP NW GW 2.0 standalone installation then please install SAP NW 740 system! That is all you need to do, 
no additional GW component add-on installation is required!! Yes, that is right NW 740 contains GW 2.0 within it and also it has SAP_UI component by default!
Hope this clarifies.
Regards,
S Sumanth GV