The engineer scale is used because the architectural scale uses imperial units (1/8 inch per foot) and inches create issues with metric as well as make dealing internal calculations a bit more cumbersome.

"Start dropping pipe in at a slope" can be done by starting with a slope to the initial pipe placed.  Fittings will take on the slope of the pipe as they are added - as long as you continue in the same direction.  Slope for branches or changes in direction will need to be "initialized" to set the slope for the branch direction.

I like using the UHP Route Lines program in conjunction with the Design Line Trace option.  Route lines are used to layout the pipe run centerline  - complete with slope -  and are exploded before using the Design Line Trace option to generate a matching design line - one which allows multiple slopes on the same Design Line which will fill completely providing the user has a valid layout. 

Here is a link to a video showing how this is done: https://youtu.be/LTIwLfvcznk

I also "wrap" CADmep content using a different software package and then populate route lines (sloped) which allows me to add individual fittings without using the Attacher and place them fitting-to-fitting or anywhere along an existing pipe. 

Here is a link showing wrapped fittings: https://youtu.be/sJZpCm9j43c