How do multiple Tivo's Work?

I understand that with the bolt, which has 4 tuners, I can connect tivo minis and watch using one of the tuners on the bolt.

Now, what happens when I have multiple Bolts?
1.) If I had two bolts do I now have 8 tuners?
2.) How does that affect my tivo service? Do I still pay just $12.50 per month, or do I have to pay double that at $25?

Thanks