There's a deckmud calculator at
www.johnbridge.com, where they specialize in this sort of stuff, rather than a generalist site like this.
What you've described is not ideal. You normally want the drain in the middle of the floor (unless you are doing a linear drain, where it can be at any edge, or in the middle, or actually nearly anywhere in between). The reason for this is you need 1/4" per foot from the FURTHEST point from the drain, and if it is near an edge, that slope from the 'short' side will be MUCH steeper. So, say the drain is 4' from the furthest corner, that means it must slope down 1" (4' x 0.25"). THen, if it is only 6" from the edge, it has to rise that same 1" in only 6", a very steep slope. The alternative is to keep that slope at 1/4" per foot, but then, the bottom edge of the wall will vary all around the shower pan - most people like it to be level around the bottom of the walls, and it's a lot easier than dealing with a taper all of the edges with no two tiles the same. The preslope can taper to nearly zero thickness over a slab, but normally would need to be thicker over a subfloor. The setting bed needs to be closer to 1.5" thick for best strength (it's not bonded to anything), but 1.25" over a slab can work, but more is preferred.