Are there roots penetrating?

I'd spend every dime you have on a replacement roof, HVAC repair/replacement, moisture control, and then tackle a kitchen or bath if the budget supports it. 

Again, something your insurance agent is going to scrutinize.100+ year old houses tend to have dirt floor cellars (or crawl spaces), so moisture is a thing in the house. 

The seller had conveniently failed to disclose the frequent roto rooter calls to unplug the sewer line that was penetrated by tree roots.

This will let you know if there are any plumbing leaks or any clogs in the sewer lines.2nd look at the foundation very closely, look for any stress cracks and see if any moisture coming in.3rd check out the HVAC systems.

So my sound proofing is focused in the second floor/ceiling of the first floor.For soundproofing, I do the following;1) I am mindful to seal up all of the second floor subfloor penetration.2) I installed 3" thick mineral wool (Roxul or Rockwool) insulation between the floor joist directly above the sheet rock.3) I use resilient channel to hang the ceiling drywall, which is 5/8" thick (per code for fire barrier, but is a bonus for sound).The above does a good job at reducing sounds like TV's, radio's, talking, etc.  

That stated, I'd sure like to find out why the OSB failed from moisture issues as it's supposed to hold up to weather.

Well they make their money selling moisture barriers and whatever else.

Clays shrink and swell depending on their moisture content/plasticity and you don't want your foundations to do the same.

Have water, fire, moisture, temperature, motion sensors, voice interaction with customers, throughout the systems.