spray foam insulation will cost more but stop air infiltration,
elminate the need for a vapor barrier, and has a much higher R value
per inch. you would need it professionally installed, since you will
need a lot. it also helps cut noise transmission and wuld be a asset at
resale time.

whatever you do take photos of all walls and cielings during
construction for later reference to electrical plumbing and other
utility locations.

have fun, I enjoy stuff like your doing