Hi,
you can keep your business suite on NW 7.00, you have to install only IW_BEP component on it, then you will need standalone NW 7.31 server (no business suite!, just only plain NW 7.31 or 7.4 with gateway and UI5 component) and then ask your basis team to connect these 2 systems. Then you can develop oDATA services on business suite system, expose them to gateway system where you can develop the UI5 part of the app.
Thanks Jiri