What concerns should i have about moving into a 100-year-old nj farmhouse?
If it's painted and that old, there's going to be lead paint, lead window putty, etc. 

You'll not "really" want to to but really should investigate the septic arrangements, and get whatever it is pumped out and inspected. Water testing should include things other than lead (with the prime one being coliform bacteria, the most basic well-water test.)

Any old house will keep you from getting bored; there's always more to fix than you have time (and usually also money) for. 

You'll probably end up replacing the electric wholesale, eventually. When you do, remember to run network wiring (or better yet, conduits for network wiring, since it tends to change over time, and being able to pull it out and replace it is golden.)

Rusty cars can usually be vanished with a call to the scrapyard - you might even get $50. Unless they are something with value to a collector (even in rusty condition,) that's probably the right call.