As the only place where the Holy Land could be crossed without climbing mountains, the Jezreel Valley was home to important trade routes and thus, was the site of many important battles between Middle Eastern powers.
In Biblical times many wars were fought here between the Israelites and their neighbors, particularly the Philistines.
The Christian "Armaggedon" refers to the city of Meggido in the valley.
In the year 1260, a Muslim army defeated the Mongol Empire at Ain Jalut (now Ein Harod). It was the first ever Mongol defeat and marked the beginning of their decline.
There are buses from Haifa and Tel-Aviv to Afula and Migdal Ha Emeq, many of which continue north to Tiberias and other Galilee cities, but bus service to small towns and villages off the main roads is few and far between.
The best option.
Hard to bring this issue up, but Jenin is part of the PA, so you'd probably need to consult them after crossing the checkpoint into their area of control. As far as I know it's quite safe for anyone who can't be mistaken for an Israeli.