Roof is shingles, on top of what, I don't know. Attic is exposed so I can check up there, though its got a lot of history on it... Might leave some "indicators" (TP with marker that runs when wet) in areas that look (recently) suspect.

My bigger concern is water getting in other places - noticed some rot in a couple window sills, which jut out considerably, along with the window frames themselves.

Luckily plumbing is only in the 1850s wing, and not over any of the original structure. But it is certainly a problem, given the number of patches of exposed and degraded plywood I can see while precariously perched on a listing toilet...

Golf ball will confirm and quantify floor slant, but what then does that data tell me?

You have bought a money pit. Be prepared.

My suggestion is start with things that affect the structure of the house, water infiltration is the biggie, rot and insect damage.Get a good book on repairing windows and frames and use it to save those irreplaceable windows. The golf ball test will tell you if there is normal settling or insufficient floor support. As for the yard the most important is to ensure that the yard drains away from the house. These areas need immediate attention. Then tackle electrical and plumbing, depending on your capabilities consider using professionals.

Live with the house before tackling the ascetics. You may find that will give you time to imagine better ways to tackle issues. Some pics would be great to see what you're dealing with.

Your BIG need would be to get a roofer that has worked on old houses to evaluate what you have for a roof. And fix it ...

The rotting windows - probably caulk fell out and was not replaces, or the slope of the sill shifted and was not fixed.

One option for a journal / log book sort of thing is Owner Builder Book. They have construction journals from people who are working on their own projects without a contractor. My dad has kept several when working on our houses, and although they aren't the most aesthetically pleasing website, it may be a good fit if you are looking to write about your projects.

https://www.ownerbuilderbook.com/blogs/

The good news is that many of the bad things that might have happened already have. If the roof is tight my primary concern would be bugs. Termites in the sills, and anywhere else, powderpost beetles, and or carpenter ants.

I'd start in the basement and work up to the attic poking around with an icepick to look for soft wood, looking for any exit holes from powderpost beetles, unexplained piles of sawdust, mud tracks up any of the walls, or any of the other signs of bugs.

Sill replacement would be the most common need on a building like this, fortunately it is not as hard as it appears initially if the foundation is sound.

Uploading pictures is such a pain, sorry for poor quality, just a quick sampling of what I'm dealing with.

view of the roof from the attic

north side of the house

south side; seems odd the windows are so proud without any roofline overhang

first floor, south end, old water damage

first floor, drooping ceiling

Thanks everyone for their feedback so far

Love your photos. Your primary concern is water infiltration, as others have said. That means check hard, and repair/replace the roof. Also, double and triple check the slope of the yard surrounding the home and make sure it drains away from the foundation. Then when those items are taken care of, you can start repairing window sills, sashes, door sills etc. If you want a book that touches on many different aspects of the old home evaluation and repair, consider "Renovating Old Houses" by George Nash. Our copy is very worn and proved quite useful at times when we redid our 1838 home.

Most of your photos show little of concern to me. DO NOT let some roofer convince you that you need a ridge vent. They'll either install it, and it will be useless or they'll cut into your ridge pole. Whatever ventilation the house has had for the past 300 years was/is working just fine. And DO NOT insulate.

The photos of the interior mostly just show plaster that has broken keys. That is quite repairable.

Finally, I'd say that the peeling paint is from one of several possible causes. It could be water infiltration. Pay extra attention to the siding to roof transition. Your next possible problem, is that some misguided person may have plugged up vents/cracks that allowed the interior air to flow up thru the house. Now the moisture created by living is migrating thru the walls. That could be the cause of the paint peeling. The last possible issue could simply be poor preparation prior to the painting. All areas must be scraped down to bare wood or a very firmly attached prior layer of paint. Then apply high quality primer and re-paint.

Good luck and check back here often. Many of us will enjoy following your progress.

My experience is with the 1820 cape I have owned for 10 years. Some words of advice.

1. You mention the drystack foundation. Is it mortared? My house has the typical fieldstone foundation. When water started to intrude, I had a mason come in to repoint with new mortar. Then, as recommended, look at gutters, downspouts and grading away from the house. Problem solved to the point that when great rains flooded all of the neighbors' (new house) basements, mine was bone dry.

2. Stay away from new house contractors! The house has withstood time using a style of construction and old systems that are both tried and true and largely incompatible with everything an experienced new house contractor knows how to do (and will recommend to you). Old houses need to breathe. That said, some new ideas work well. Have someone take a look at your chimneys. Old houses can be drafty if you are in a cold area- but a new liner and a wood stove more than compensates. Crumbling chimneys can be addressed and flashing at the roof can be a source of water intrusion.

3. Look into a contract for pest control. They come out every year and scope out the situation and take care of issues as they arise. Mice were a problem for the prior owners, with cats, the mice are not a problem.

4. Good job on the windows! Keep the originals. If I had one piece of advice it would be Keep EVERYTHING. Someone will come along and wish you had.

5. Paint on the North side looks rough- but in a cold winter climate the North side is beaten up and also given the least amount of light to dry things out. Your house is white so temporary spot priming is an easy option.

It looks like you have a really amazing house. Love to see more photos.