Your rule of thumb is ok but in all likelihood could be funded less expensively through the use of an excess liability (Umbrella) policy.

If you have a million in assets you would get the minimum requirement in the auto that would allow you to get the excess policy and then the excess policy for a million. Experience tells me that it is about 300K minimal for the auto liability. You do need to have Homeonwers Insurance as well but a house is in your rule of thumb.