IDK about the locations. You are talking about fans for the NC teams, paying for a "bowl" ticket, then a NC tickets. It would be pricey for the consumer. I think you have seeds and top seed gets homefield until the NC. JMO.
That's a great point. Have the first two rounds at the highest seeds' home stadiums and then the championships at the bowl sites. That would work much better for the fans. I guess the other option would be to play round one at the home sites and then play the final two rounds at the bowl site. Make it a week long event. Weekend #1 the final four teams play two games at the Bowl site, then the following week the final two teams play in the championship. Fans could make a full week vacation out of it. It'd be a helluva lot of fun!

The key to this is to not let the system be driven by existing bowl games. Think the NFL model ... The higher seed plays a home game, begining with all conference championship games. This removes much of the travel concern. The championship game can then finally be played in one of the bowls similar to how they rotate now with the BCS.
This should be thought of like the NCAA basketball tourney and the NIT. The football playoff is separate from the lower tier bowls which can still be played outside of the playoff system.
The big issue in this is not the fact of the playoff system itself. The issue here is who holds the knife when the cake is cut.