Mobil 1 and a Mobil 1 oil filter will be just fine. I recommend using a good engine flush (AMSOIL or BG come to mind)first, but if you don't, or won't, flush, plan to change the oil filter after a couple of thousand miles. And depending on how the oil looks (or tastes) and whether or not you get increased oil consumption, you might want to change the first batch at 3-5,000 miles.

I believe a 19mm wrench is all it takes. I've never had a a problem with the oil drain plug.

Cheers

When you say Mobil 1, do you mean in the engine?

I didn't know Mobil 1 made an engine oil filter for the 850. Just my opinion, but I think it might be a better idea to run the OE filter. Lesser chance of leaking, designed and specified resistance and filtration. Just my opinion though.

As for running a good synthetic like Mobil 1 after 100K miles, I don't forsee any problems except that you may notice a little extra leaking and consumption. Synthetic oils have a tendency to open up little leaks when they dissolve the sludge and deposits built up over the years, and to make it into areas it's not supposed to on older/high mileage engines. So just get an extra quart for top ups. You should be fine though, I wouldn't worry about it.

As for a special wrench for the extra large oil pan bolt, if the 93' 850 GLT has the same size bolt as the following 850s and _70's, it should be no problem. I don't remember the size though. I just open up my tool shelf from the box, and grab the wrench with that yellow print on it :)

As for the CD changer jam, do a search. There was a recent thread regarding this issue. I have a different changer so I wasn't really paying attention to it.