If it squats you may need heavier Rear springs. The one's the install are 400 lbs (i think) Especially since your from New Jersey and the roads you travel.
Summit has a mat that's cheap that you can install and remove to get the bugs out.
Front end shimmy is probably tires. Especially since it doesn't do it below and it goes away above that. Mine does the same i can tell hoe fast I'm going. by the shake, and my car is totally smooth at 92.
And the rattle that comes after driving is your ear drums
because most rattles don't go away and come back. Baffle shake would probably remain constant.