Greetings!
The 5130 switch series does not provide a backplane stacking capability; if you want to stack these switches, IRF would be the means to do so.
As far as mixing switches in an IRF stack — you can use different models within the same switch series (e.g., all 5130 EI or all 5130 HI, but not a mix of both), as long as all switches in the fabric are running exactly the same software build.