Your profile says you are an architect. That means you know there is more to properly building a home than simply ordering a package from the local lumber store (with the appropriate engineering stamp) digging a hole, pouring some concrete and than commence hammering nails.I'm starting to remember why I haven't been back to this place in months. Nothing can be done. Nothing is possible. Do you guys actually get out of bed in the morning?
Some people have done it this way, even without buying the package deal and not have the bedroom floor fall in when the waterbed was topped of the first time. The same situation exists with homebuilt airplanes. Some people get lucky. Others, like one that hired my architect grandfather to figure out how to put closets in the house he designed himself because he 'forgot' that little detail, aren't so lucky.
Aircraft are every bit as complex and full of little 'gotchyas' as any building. There are some very smart BTDT individuals here on HBA. Their advice may seem like they are saying "don't bother" at times but that advice comes from experience. It is offered not to dissuade but to prepare.
You can't separate the number produced from the manufacturing/startup cost. Selling only 10 widgets means that manufacturing methods and materials that would be cost effective if selling 10K widgets are not possible.I'm going at it from the perspective of how much is it going to cost to get started and into production before I decide how many units I will need to sell