For the vibration, lift up the front and check all the steering components. Ball joints, tie rods, pitman arm, idler arm, steering shock, strut rods, sway bar links, and bushings. It's pretty likely the shock is bad, and a lot of people overlook the idler arm which attaches to the frame.
I don't know if you were planning on having a mechanic do the work, or if you're doing it yourself, but if you have a place to work I would suggest learning to do the work yourself. You'll spend significantly less than a shop will charge, even if you buy all the tools for the job, and the knowledge will come in handy on the side of the road
Definitely get that rust out of the way first if you can. It's always the most intimidating part of an Eagle project. Everything aside, it looks great and I love the SX/4s!