You need the car long enough to be able to make sure that it suits your lifestyle:
Can you get to work and back on a single charge – or can you charge it enough while you're there to make the return journey?
Once you've got home is there enough left in the batteries to make your regular evening trips – children, sports, shopping – without a recharge?
If you only make shorter journeys how often are you likely to have to recharge – and what would be the consequence of forgetting to plug the car in one night?
You will also need to find out where public charging points are located – particularly in and on the way to places you might visit frequently.
Check with your employer too rather than assume you'll be able to charge the batteries while you're at work, if that's in your plan.
Cold weather, use of electrical items such as lights and heaters, and carrying loads/passengers will all reduce the car's range on a full charge as will a heavy right foot.
To get a good idea of the car's true range:
Drive as you intend to drive normally
If you regularly carry passengers take them with you on the test drive
Switch on everything electrical