SAP FIORI installation senarios

Hi Experts,

One of our client want to implement SAP Fiori to their existing environment.

They want to install Fiori-Dev environment with minimum H/W resource.

They want to use existing ECC system as source system for Fiori. but do not want to install Fiori add-on on it.

My Question is, in Fiori Central Hub Deployment scenario,

1)Can we install SAP N/W Gateway server +Fiori add on system(say N/W 7.4) as a standalone Fiori system and connect it to Existing Back end ECC system using RFC's.

if Yes, What is the method used to connect Back-end system with Fiori system, where Fiori add on will not be on Back-end ECC system.

please help us to choose the installation scenario

Thank you

Sreekanth G