I am wanting to build a house over time and was wondering what you guys thought of this idea.

Wrap a "Lumber link" http://socketsys.com/ system with SIP.  My reasons are the following.

1.  Would have a barn feel inside but be super insulated.
2.  Once the building was "dryed in" I could take my time with the inside. 
3.  The entire inside would also be hollow because the Lumber link system would support the SIP.

Excellent idea. I have looked at this system myself, and will again.
Have done several 'pole barn' type structures with SIPS. Have one under construction now.
Great, economical alternative to timber frame.

Another question. Lumber Links offers two different roof styles Gable or Gambrel. With all your experience with building SIP homes and roofs would the Gambrel roof add cost and complexity to the job vers Gable? Just seems like Gable would be the better choice for install ease and ordering.

The gambrel would be more difficult to construct. But it gives more usuable living space 'under the roof' compared to gable roof. If you like the gambrel style, I doubt that the actual installation would be that difficult. A few more pieces to handle, and cuts to make. Overall, if you like the look, and need the extra space, go for it.