Re: questions about remodeling 1914 house
Drywall can't replicate real plaster.
Decide what "look" you want...and then hire a pro for minimal damage. HVAC goes through attic spaces and is ceiling work.
However, there's a case for change when you want to upgrade your insulation, and/or when you want to add audio/video cables, etc... I would bet that your utility savings will pay for the change over a few years.
CAUTION: if you decide to change to drywall, MAKE CERTAIN your floors are leveled - or flat - BEFORE drywall install. Our previous owner changed without doing that and now we're facing many wall repairs after leveling our floors. What a pain...