A typical way would be simply to duplicate the bottom edge of the wall, and convert it to a curve, down which you can sweep a profile of the molding.
ShiftD Duplicate the bottom edge of the wall
P separate it into its own object, and Header > Object Menu > Convert it to a curve. (The 'Path'). Make the path a 2D curve, to ensure clean miters.
Construct a ...
I think you should get something pretty good with sculpting, you just need to observe how the fabric behaves. Here's a quick try, I've given the object a Multiresolution modifier, when you're fine you can bake the normals, delete the Multiresolution modifier and use the normal map on the original low-res version.
You have to joint the objects to one and then apply the modifier and then you can separate by loose part...
or apply the modifier to one then select all others and then the one with modifier at last then ctrl+l to copy modifier to all selected
I've just looked back at the files I saved at the end of each video (under Windows 7 using Blender 2.80 final):
Part 2 around 607KB
Part 3 around 678KB
Part 4 around 679KB
Part 5 around 10,210KB
so there's a jump during part 4 of Level 1, but nothing like you report and in fact the final Level 4 file is under 14,000KB so you've done something wrong ...
So, I finally made a blender addon that solves the save problem by first saving the .blend file to the temporary files location, and then copying it to the network share.
Right now it works by remapping your ctrl+s or cmd+s shortcut.
You can find the plugin here: