Originally Posted by bobjob
i'm guessing that you aren't using your wife's sewing machine
You are right. Here is a shot of the sewing machine I got for doing the interior. It is a Tacsew T111-155 with a walking foot, compound feed, and a 1/2" of lift under the presser foot. It was $950 delivered to my door which included a 3/4 hp servo motor (highly recommended for the beginner).
I'm a total rookie at interior work so others can better answer your specific questions. But from what I've read on prior threads, it is not out of the question to do an interior using a common, household sewing machine. The biggest problem will be getting the required foam and fabric to all fit under your presser foot. That is why I mentioned above that the Tacsew machine, like many other upholstery machines, have at least 1/2" of "lift" under the foot...so you can get many layers of stuff under there to sew at one time. Household machines normally allow much less clearance under the foot.
But with some well thought out design and planning, many say it is possible to do it with a household machine.