If I am correct, the amount of cameras that you can have with a Nest Aware subscription is ten. However, I can't find the exact information on the site at the moment.
You must be aware that you will possibly need a robust wifi network to handle those six cameras. Myself, I have a 400 Mbits Internet connection, a wifi extender, and my five cameras work fine in my 1 187 square feet house. Depending on your Internet connection, you could have to upgrade it, and/or add a mesh wifi to your house installation, to handle all of your cameras.
