what hot water system to use?

[KatM]

My house is a standard 3 bedroom, 1 bathroom, 1 kitchen, separate small laundry single brick veneer home, built in 1939.  I will soon be having a refurbishment done and in addition will ve upgrading the HWS. 

I would like electric as I'm looking at getting rid of the remaining gas items I have (which us just the stove and HWS).  

Once the refurbishment is done, I'll be renting my place out. The home is likely to fit 5-6 ppl (family) as I may also be getting an additional pod out the back. 

What size HWS should I get? Ideally electric. Is a heat pump needed as well? I ask, as a few ppl have mentioned this. 

What does bunnings have in the way of the above? 

Does anyone know if I can also get the government rebate?  TIA