Sorry, but I've got to chime in here.... Al, you have to realize that the vast majority of the shade tree mechanics will change their oil every 3000 miles using whatever's cheap from teh local parts store. It's what we've done for generations, and will likely continue to do (especially on those vehicles which were designed with that OCI in mind.) In the absence of monthly oil analyses and an expensive bypass filtration system, a 3000 mile OCI is simply the way we do it because we can be assured that the oil is in decent condition when we change it. For most of us, it's not worth the hassle to swap filters, top off, send out the oil analysis and wait for the results when, in 20 minutes for $15, we can swap the oil and be assured we're good for another 3000 miles.
Rather than question everyone else's motives by asking 'why' just accept the fact that it's what we're told to do by the manufacturer, and in the absence of any other reliable source of data, can't you accept that it's just what we're gonna do?? Yes, you have a better way. Yes, using your setup, most people could probably go several years without an oil change. Not all of us have the time, the funds, or the desire to do anything different than what the engine manufacturer recommends.
Sorry for the rant... It just bugs me when Al chimes in and just questions everything about oil changes without actually helping the OP with his/her questions.
Now, to the OP, pick up whatever oil you want from the parts store. I personally prefer to stick with name brands myself, but so long as it meets or exceeds the manufacturer's ratings (and I haven't seen any that don't), and use a decent quality filter (motorcraft and Purolator come highly recommended) and change it every 3000 miles, it'll work just fine. Hell, I'm convinced you could run a gallon of canola oil through it in a pinch!
For spark plugs, my preference is Motorcraft. They were good for the first 100,000 miles, the second set in mine has 72,000 miles on them, and when (if?) she rolls 200k next year, she'll get a third set.