Some houses don't have 3 phase power, so for those having a 3 phase inverter is pointless if they can only use one of the phases.
You can also go the other way and install a single phase battery backup in a 3 phase wired house. If all your important loads happen to be on the same phase you could battery backup just that 1 phase. You can also rewire your electrical panel to have all the important loads grouped onto a dedicated input feed, then run only that feed trough the battery backup transfer switch. This way you can avoid having very large loads that are not quite essential in a blackout being backed up (might drain the battery or blow fuses if the inverter is not rated for enough power)
Charging a electric car is a bad idea. The car likely has a pretty huge battery pack in it and charges at a pretty high rate, so it means you need a powerful inverter to handle it and unless you have an absolutely massive battery bank in your house, it will drain the emergency power very quickly. The car already has a battery built into it, just keep that battery charged up.
For charging up the electric car a regular gas powered generator is a better idea (as ironic as that sounds). Storing hydrocarbon fuel in fuel canisters holds a lot of energy on the cheep. In a more extended blackout you can also use your car to go fill them up at a gas station and bring them home, then use the generator to charge your homes emergency battery back up. You still get a lot of benefit from the houses backup battery as the generator does not need to run all the time to have power, and when it does run to charge batteries, it runs at full load where it is the most efficient. (Keep in mind blackouts offten happen in bad weather, so solar might not be making much)