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For the insulation, check out USA Insulation.
This is what they do and apparently it works extremely well. check this link out:
http://usainsulation.net/insulation-services/spray-foam/
Higher R value than regular fiberglass insulation in walls and attic.
Worth looking at.
There is a company that makes a stairway lift for older people to sit on a chair and ride up tot he second floor. They also make a small one person home elevator. Only in your case it could from your living level down to your basement and back up .....
EASIER than going up and down stairs....
That's what I had in mind.
As to the interior walls, the more clear view you have in your living areas the larger the home will feel and you will enjoy it more.
Sort of a semi- open concept that makes the house not so much of a cave. Just something that most people today are looking for....