i will attempt to satisfy a couple other questions. my use of tippet may not be correct.
correct; backing, fly line, leader(tippet), fly.
i believe the loose criteria for backing is to provide low memory, improved abrasion resistance and break at a poundage greater than your tippet. often a braided type line accomplishes this, as for you question about a special type of backing i am not sure but would imagine if it follow the aforementioned guidelines it can accomplish the job of filling the spool and providing additional line for when you need it.
there are a couple knots you may want to familiarize yourself with. there may be better options but i was taught to use the following; attaching the backing to spool i just use simple double knot. if for some reason you find yourself in a situation where becoming spooled by a fish is imminent just palm the real and force the weakest link(should be the knot attaching to the fly) to break.
to attach the backing to the fly line i use a double nail knot.
you put two of these together and when you pull the two lines together the two nail knots pull together. this knot creates a more streamline option conducive to flowing smoother through your guides of the rod.
i attach the leader to fly line using the same nail knot; for the reason named above.
i use a tapered leader for the first several feet of my line from the fly line end. i then proceed to add and remove several sizes of tippets in order to control the length and strength of the tippet. i use a blood knot when changing more similar diameters of leader material(tippets). if you try to jump to big a diameter the blood knot does not work well. for example: my tapered leader may taper from fly line diameter at the junction with the fly line to about 12lb diameter or so. i then add a section of 0x or 1x tippet then skip a size to 3x for another section and often finish with a 5x-6x pending what i can get away with. do not feel compelled to add tippets unless your leader becomes to short(in your perspective). it is only when mine becomes too short that i will add the reduction in tippet materials to increase the overall leader length.
i alluded to it above in the discussion about making the backing at least rated for the estimated breakage at the attachment to your lure/fly. knots act on a line like a guillotine. a good example to illustrate my point is think of a simple overhand knot. as you tighten it it chokes itself. i have read a simple overhand knot reduces the effective breaking point of the lines rating in half; i call it a 50% knot. so the obvious solution it spread the pressure of the knot over a larger surface area. a good knot will exceed 90% of the lines rating. the key to takeaway from this is the knot at the lure/fly should be weakest link in the system.
i may come back later and address any ambiguity's i have created or try to address any other questions/concerns you may have.