Lots of questions...there are a bunch of tested, approved methods to build a shower. Over a concrete slab, I would not use wood as the curb...I'd use brick, pavers, or a premade, tileable curb...two reasons, treated wood tends to be quite damp as delivered and can twist into a pretzel and crack as it dries out. The other reason is a slab may allow wood to wick up moisture - it should not get any from the shower if it is done right. There are basically two methods to build a tiled shower: conventional clamping drain with a liner; and, a surface membrane shower. They use different kinds of drains, so this decision needs to be made at the beginning. Ideally, you'd have the drain in the middle of the shower, but if it isn't too far off, it can still work. The goal for most shower builders is to keep the bottom edge of the shower tile even (level) all the way around, and if you do that, the further the drain is from the middle, the shorter side needs to be steeper. Redgard wouldn't be my first choice for the liner. If you're going to build a conventional shower, a pvc sheet liner is cheaper. A conventional showerpan is made up of 5-layers: a deck mud preslope (deckmud is a mix of sandortland cement in a 5:1 ratio or so mixed with enough water to make it stick together if you squeeze a handful, but not drip water - it packs like wet beach sand, it's not like concrete and pouring it will only make loose lumps!); a liner; a setting bed (parallel to the preslope); thinset; tile. The details a numerous, and failing to perform one properly can lead to failure. The golden standard for this sort of stuff is the TCNA handbook (Tile Council of North America) which lists the tested/approved methods. They do not list brands, only types of materials. I'd also check out www.johnbridge.com .