I believe there is a special full catback exhaust made specifically for Sport Trac's that is available to you. "TruBluSportTrac" knows what it is specifcally, I just tried looking for it but no luck. It's reasonably priced as well. Depends on "how far" you want to go with the exhaust mods.
You don't have to buy a tip, it would just be the end cutoff of the piping. There is no "stock tip" unless yours has a stainless steel tip welded onto the end, which I haven't seen any Ford car off the lot with these on unless its something like a Cobra or Lightning.
I'm not sure about the emissions, it should pass, but I dont know. Once TruBlu chimes in here again then I'm sure he can tell you more info such as the manufacturer + other stuff.
I've ordered an exhaust that was designed for the sport trac (the only one designed for it and nothing else). It is made by Random Technologies (more well known for the high flow cats...also available). I ordered in through Martel Brothers. It is supposed to be the quietest performance system available and also has a "tip" similar to the stock set up. Good luck on your search.
Another informative website is www.mysporttrac.com . Their are a few thousand members and if you want something, odds are that one of them has it, or has had it. Again, good luck, and welcome to the site.