I would say be careful placing your talents and skills on others. While sculpting a bed may come easy to you it doesn't to a lot of us. I can take a photo and draw it in pencil and it virtually looks like a black and white copy. I just get it. I see and my hand draws it. But I would never tell someone that it's easy, just easy for me.The pre slope doesn't have to be perfect---a proper mix helps---makes packing the mud easier---
For the top bed---I simply scribe a line around the pan where I want the wall to meet the pan----and start packing----never tried the plastic gizmos mentioned earlier----couldn't see how they would help---it's just not that hard to sculpture a pan with the wall line and the drain set to work off of.
I always use a square drain cover---Cutting into a round one is much more difficult---
The pitch perfect gives you the perfect pitch from the walls to the drain every time. I know plenty of very talented tile setters who use them.
To the op installing the liner without a Preslope is wrong. Subfloors are level and you need the liner to direct water back to the drain when it reaches the liner. Otherwise you are creating a pool for nasty water to sit and fester. I just pulled a pan done this way and it was nasty. It's the plumbers way of doing it and old school thinking.