I am weighing the prs and cons of

Ive always found having a 'scaldino' for the kitchen (10 litres)  and another (30 or 50 litres or even 80) for the bathroom is the most economical way to go.   A scaldabagno uses 1800 watts, typically - but having the tanks near where the water is to be used means no waiting for the hot water to come through,  and the scaldino under the sink if it is left on, uses very little electricity.    If you have a single hot water tank, you will have to sort out hot water pipes from your bathroom to your kitchen presumably.   An instant hot water heater probably doesnt give enough pressure for a shower to work well, whereas a 30 litre tank will give you enough hot water for 2 showers and a 20 min reheat time.    

In Puglia a scaldabagno normally consumes 1.2kw, we had ours on timers. (Some say an instant gas water heater is cheap to run but changing bombole is a fag). However our main source of hot water was a 200 litre solar set up with an integrated electric heater (1.5Kw) for winter operation. If you want to keep costs down, maintain a 3kw supply and use electric scaldabagno. One drawback with an electricly heated tank is that as soon as you run hot water it begins to fill with cold water so you never actually get as much hot water out as it says on the tin... good luck!