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. 

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.

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.  

Any rust or moisture on the metal will be like a cancer and it will continue to rust between metal and patch, and eventually the patch will fall off.

It's pretty common for REOs to smell like they have a mold problem when in actuality they don't -- once you get the HVAC running with a decent filter, the smell will go away.That said, if there is a mold problem, the first course of action is going to be to determine what the source of moisture is, and get it remediated.

In addition, increased potential for moisture damage and fire damage.