You're being charged almost $60/mo just for the boxes alone? Weird.
1. Not sure. Some fees may be part of the service. Some fees may be tied to the boxes. Fees tied to the boxes may go away, but fees tied to the service could remain. Basically only they could answer that question. Ask them what your final bill would be if you rented 2 cablecards instead.
2. Cablecard rental fees vary but are generally cheap, between free and $4/mo each for the cards. You may need to ask them what your final bill would be to see what fees, if any, they tack on.
3. As a newbie, it might make sense to just get one $150 Tivo Premiere with $15/mo service to start out with. Or there's a 4-tuner model for $250 if that sounds attractive. See how it goes first. Return it within 30 days if you don't like it. Get another if you do.
4. Tivo can't access VOD unless there is a deal between them. In the case of ABB, there's no VOD access. But Premiere boxes have Netflix and Hulu Plus streaming support built in, if you're a subscriber to either of those.