My Contour SVT was 'supposed' to be 100,000mi interval for plugs. No way. After 30,000 the engine was very happy to get new plugs. (particularly in the front bank, where the spark was reversed, so the ceter electrode wore out fast.) (( in the Focus, I think all four are direct spark ,so the ground wears more. I am not certain about that though. You want the ground to lose material, not the center))
For the filter, I just use the Motorcraft with the 's' silicon valve thing.
Filters are pretty much the same as the videos showed on the link above. The major difference is price and name.
So I buy the Motorcraft as they are decent, and only $4. The oil is a different matter, and i use Mobil One, and now the Mobil One Advanced Fuel Economy oil. It is only in 0W20 but the '0' is just better cold fluidity than '5', and since i live in the Northern climate. no problem. (I am more of the buy good oil and change it, than buy a premium filter and leave it in forever!!)
So far i have changed my oil twice. First at 1,000mi but I could not get the OEM filter off. So I skipped changing it. Then i decided to change it again !!! at 2,000mi and also did the filter. So now I am set for awhile!
Yeah I am crazy and wasted resources.. At least i recycled the used oil instead of pouring it down the sewer..