Post-tension slabs are more common in earthquake country than elsewhere, but could show up anywhere. There would normally be some warning labels plastered around in places you'd notice them if you had one, but there's no guarantee. If you have them, it's very dangerous to start cutting up a slab.
Running water lines in the slab aren't a great idea either. As to drain lines, they usually try to run them underneath the slab, not it it except to come through it where they need to be. While drain lines can leak, a water supply line is probably more problematic. PVC is pretty stable and should last a very long time, but copper can be eaten up by some soils, and fixing a leak beneath the slab is often costly and inconvenient...I'd keep them in the walls.
While possible to leave your shower drain where it is, it's problematic. Most people find it much better looking if the pan has the same height all the way around the shower. This means that if the drain is offset, to maintain the minimum of 1/4" per foot slope, the longest distance from the drain to the wall determines the amount of drop. Say it's 4' on the long side, that equals an 1" drop. But, to the short side, it may be only 1' (maybe an extreme example, but you should get the idea). That means instead of 1/4" per foot on that short side, it will be 4x steeper since the drain must be 1" in that one foot below because of the long side's slope requirements.
Once you get the plumbing figured out, check out www.johnbridge.com for help with tiling things and building the shower. Look at www.schluter.com and their Kerdi system...really slick.