You got an exceptional deal. It's an excellant processor. You can use the fourth slot either as a quick rinse or for two stage fixing.
RC paper is resin coated paper, it has a plastic coating, this makes it much more resiliant and easier to handle. It is also much quicker to process and only needs a few minutes wash time.
Fiber paper is uncoated. For some reason it gives a bigger spread of tones and has more depth. Some fiber prints seem to have a jump into the picture look to them, where RC can look flat in comparision.
Fiber paper is slow to process, fragile (as it soaks up the chemicals) and difficult to wash.
I do all my general 10x8 inch prints on RC paper. If I want stuff to add to my serious portfolio or for display I grit my teeth and get out the 12x16 inch fiber paper.
You also have a choice of VC or graded paper. Most folks go exclusively for VC these days.
Try to find as low a consitiant temp as you can for the fiber paper. You can lose a bit of the tonal spread if you increase the dev temp. The 12x16 RC paper I sonetimes use I also do at 20 degrees as it's difficult to get it quickly from slot to slot. The 10x8 RC is all done at 30 degrees C, 30second dev, 10 second stop, 15 second fix.
You can I belive get fiber paper through the quad with a little experimentation and care.
Oh and don't forget the selenium for finnishing your prints.