What [NOW] should I check or have checked on my Dodge Neon ? Please answer much as you can. Thanks !

on the first part of your question check the vacuum lines coming from the tank on that one,the ones the connect to the canister tank in the front may be loose or dry rotted that was a real common problem with those cars,secondly the shocks your looking for are available,but that wont totally cause your vibration on it,have the recheck the tires again,even a bad wheel will cause a vibration even if they show to be in perfect balance,the machine only checks balance up to 55 miles per hour it wont go beyond that point,and i just called advance auto and they have those struts in stock,so getting those shouldn't be a problem,on the gas mileage it may be the way your running it,they wont do good on gas over 60 miles per hour,id get the struts installed and a new alignment on it that will make a lot of difference in the way it drives we just did our car and it took out the vibration we had in it,,all your problems are minor though and can be repaired,good luck.