When you contemplate how long your bellows should be on your 11x14 please consider how heavy your longest lens would be at this focal length and make sure that you design your support members to handle and "balance" this weight properly. This includes materials deflection properties and insuring that your tripod screw is sufficiently sturdy. A bit of research as to the range of weight of the optics that you could utilize would be well advised. The numbers could surprise you.

Personally I would make sure that my rail proportions for the front standard were at least as stout as the Deardorff V11. If you need some dimensions for the V11 I would be more than willing to provide you with some data.