You can't take the sissy bar off without removing the fender struts.  And you will probably scratch the fender anyway taking the fender struts off.  Make sure you get someone to assist you in getting the fender struts off/on.

Of course, if you actually mean the pad on the sissy bar (back rest ?), it can be removed by itself (two screws under the suzuki plate).

As far as the luggage rack - those actually made for the Savage mount on the sissy bar.  So removing the sissy bar would not be needed (so you must have something different - if so, post some pics when you are done!).

The luggage rack from Suzuki can be put on without taking anything off.

I wasn't sure what you meant by 'back rest' - if you meant the sissy bar or the pad on the sissy bar - that's why the extra info.

When I put mine on, I removed the backrest pad temporarily by pulling off the Suzuki nameplate and the two screws underneath it.  The kit came with those instructions and even a strip of adhesive to put the nameplate back on with afterward.

Found at one of the local Suzuki dealerships - yes, they zip off (have never used it but in practice very easy to zip off...quite a bit harder to zip back on!)

I don't recall the cost of them but I just looked and they are manufactured by Tour Master.  I can't seem to find them on their site though.