Doing some research on the web I found that the Fujifilm FP-100C is not compatible with the SX-70.
It's made for Land-100 cameras which look like this.
What you need is integral film as sold by The Impossible Project.
I've experimented with their early batches of colour film and their fade-to-black batch using a Land 1000 camera. The results were not great in terms of sharpness and contrast, but as I understand this might be caused by the low-end camera and the early batch.
I believe TIP has fine-tuned their process of creating the film, so things should be better now.
The sample images should give you an idea of the current quality.
Answering your question one by one:
Difference peel-apart and integral film (not sure here, I've only used integral film):
Process: After a shot you shield from light and wait (up to 30 minutes). With peel-apart film you wait as well, but after that you peel away the upper layer. You can do this hours after shot is taken.
Quality: Looking at the different examples it seems that the peel-apart film produces higher contrast images than the integral film.
Size:
Fujifilm FP-100C: 3.25'' x 4.25''
Integral film for the SX-70: 3.1'' x 3.1''
Other options: Not realistically, The Impossible Project is the way to go. If you really want to you can take Fujifilm Instax and adjust it to fit the SX-70, but you'll need quite some miscellaneous stuff. If you feel like experimenting, sometimes you can find expired integral film for sale for a reduced price. The results of using such film are unpredictable.
Suggestion for a newbie: Get the Impossible Project film. It's sort of "plug and play" and will enable you to learn to use instant film without much hassle. Downside: it's pretty expensive. If you find yourself in the neighborhood of Enschede, The Netherlands see if the TIP has a sale where you can drop by. They sometimes have some left-over stock which they sell with a discount (I've only encountered this once, but who knows).
