1) Not very fast. We had an 8' nylon parachute, which, according to the manufacturer, should have had a terminal velocity of ~10ft/s with our payload size (approx 7lbs). 2) Actually, the summer jet stream is much calmer, with predicted flight range less than half of that in the winter. 3) You do not, so long as its a small (I think below 12lbs) payload. You cannot, however, launch it within 5 miles of an airport. As far as I could find, there has never been an FAA reported case of a plane colliding with a weather balloon. 4) I have no idea if there are regulations on putting live invertebrates inside the payload...I didn't really want to find out either.
Meijer 5am Major Khaaan procured. Cost -less than $5
Watching 3 Meijer employees attempt to remove a snail from the tank -priceless.