[jim_bee]

I don't think there is any reason why the bottom of the wall framing wasn't closed, other than at the time nobody saw the need. Closing the joist bays at the bottom will help keep out pests and drafts, and will help keep the stud bays from acting as a chimney in the case of a fire.

Yes, the attic should be vented with air intake low and air exhaust high. Do you have gable vents or roof vents?

 

[jim_bee]

Balloon framing can be fun to work with. I've rewired a couple--sometimes it's clear sailing from crawl space to attic for pulling wire, sometimes you run into blocking that seems to have been installed more or less randomly.