Very helpful again, thanks so much. I will probably not put plastic on top of the mortar then since it won't stick well to vikrell (but if for some reason I decide to I will just use very thin plastic as you suggested, but at this point I don't think I will use plastic on top), but I will lay down some plastic on the floor so the mortar doesn't adhere to the floor. I'll just use some basic quikrete mortar mix and not use thinset.
I'll use a mechanical drain then to avoid having to do work from the crawl space. That would be amazing if I can actually do everything from above!
I'll use this Oatey Drain then:
http://www.lowes.com/pd_253153-138-4...y+shower+drain
It's a 420994 which is the same, or similar, to the 42099 which you suggested I believe. Anything to help me avoid having to do work from below is a a huge help. I will clog the drain up with something when I work on it too as you suggested.
One thing I was thinking about is do you think I need to fill that concrete hole around the drain a bit more so there is more support around the drain when someone is standing in the shower? I don't think it's necessary but was just thinking about it. I have images on this thread of the hole, it is the very first post on page 1. I don't think I will close it up if it's not a big deal, but I also wanted to double check if someone thought I should close it up more with wire mesh and concrete. I just stood around the hole with the shower base dry fitted and it seems strong enough so I'm leaning towards not making the hole smaller.
I can't wait till this part is done so I can get onto the stuff I enjoy (cbu, tiling, niches, etc.).
Thanks again for you help, much appreciated!