Interspire as a self hosted autoresponder solution for multiple businesses

I recently left hosted AR and took my list with it (which saved me about $1000 already to say at least).
Got ArpReach which I regret because of number of awkward issues i having with it.
Interspire seems to be the next recommended, albeit much pricier alternative.

Questions:

1.
I rent dedicated server and looking at Interspire + (Mailgun or Mandrill or Sendgrid). I currently use Sendgrid ($1/10,000 emails plan) although it seems to be the last in people's preferred choices. Which one of SMTP platforms would you recommend?

2.
Are there any valuable alternatives to Interspire worth evaluating?

3.
Question about Interspire: I own few different online businesses and my wife owns dog merchandise store.
Can Interspire be configured so each list would function independently?
In other words I want to avoid global "{BUSINESS} = Dog Things" and have every list include: "Thank for you for joining Dog Things" type of stuff.

I want every list's settings to be configured totally independently and not share any variables.