As much as I am a take-it-on-myself kind of person (sounds like you might be too), this is one area where I would let the foundation contractor apply the external sealant.
What I would do is find a sub-contractor who specializes in applying external concrete wall sealants and lets you do the work of renting a back hoe, expose the wall and get it ready for the sealant. He should be able to demonstrate to you the various methods and materials for concrete wall sealing that are used in your area, provide a written guarentee and provide references to residential homes whose below grade walls he has sealed. But I would supplement this with homework: Internet searching, library research and conversations with a couple of established area general contractors on what they like. This will be a fairly sizable project that will cost you a few thousand dollars even with you doing much of the work.