Welcome from another NJ member. Don't know anything about the Pfaff you are looking for info - sorry. The vintage machine you have that is breaking thread probably just needs a good cleaning, oiling and proper threading.
Assuming you are working with rip-stop nylon for your kites, I would think any machine which you could use a walking foot would do the job unless you are doing lots of decorative applique on your kites. Then you might want some decorative stitches and I don't know how compatible they are with a walking foot as I don't own/use one.
Where in NJ are you located?