Had all the same problems when we purchased an '09 E-450 at the end of 2012, it had 15m miles on it. It had 3 owners in 3 years. Scary handling and dangerous.
Dealer paid for an alignment which helped except on windy days, still scary.
Spent a lot of time researching forums because I was a total newbie. Found a guy called "Harvard" on the IRV2 form, look him up as all the front end info is there. Castor settings are set at more than +5 degrees using Ingalls bushings
p/n 59400. Sage advice from him and what a difference. Since then other handling improvements include: Bilstein shocks and Bilstein steering damper,
Hellwig sway bars front and rear. Fours ago I didn't even know what sway bars were, amazing improvment. Also put in a 5Star Tune which is great for the interstates.
It is a pleasure to drive and I am thankful for these forums and the expereiences that others share.