That's not how the Internet business model works. Receiving data is effectively free. Transit providers charge the sender for the bitrate (high for the web host, low for the web user) and a fixed fee for the connection, which you will have to pay regardless. Peering is paid for per connection and often by the web hosts who want to avoid transit and get better latency to the ISPs customers. In terms of traffic, there is effectively no difference in cost between sending traffic internally or receiving it from an external source. The reason for data caps is that ultimately networks are capacity constrained, but mostly at the last mile, not at the peering and transit links.
This is totally false. Inter-AS traffic is often priced using bandwidth in peered connections. In a bandwidth discrepency situation one isp will usually have to pay a lot more for the inter-AS traffic.
Right, and that's the sender, which is what I said. Note that the amount of traffic is effectively irrelevant since the connection is supposed to be dedicated. The only reason why the amount of traffic matters is that you need to decide which side pays what.
No. Generally the agreement works like this: "we'll set up a peering agreement between us. As long as the traffic differential is within 3%, peering is free. Beyond that point, the exceeding party will pay an excess penalty of x/GB."
