The bikes look fantastic with the stock plastic and graphics.. Pick any modern intermediate tire, and you'll be fine. Before you throw money at the suspension, ride and see just what it needs.. I don't know your weight, but maybe just a fork oil change and setting sag may be fine for your type of riding. I put front and rear springs in my for my fat butt, left the valving alone and it works fine..
They are great bikes, and a ton of fun to ride.. Here's a picture of my 1993 KX125.. I'm a fat vet rider and it scoots me around wihtout a problem.