I have finally got around to doing a tutorial, in 3 parts, on the whole process of taking an asset into Blender, out to Substance Painter and back. Following a discussion with someone on the Allegorthmic Forums. Apologies for the rather long first section.
Part01: https://www.youtube.com/watch?v=-yInmaj1-tw
Part02: https://www.youtube.com/watch?v=Mxnv0CdPt8k
Part03: https://www.youtube.com/watch?v=XwFa1GQQsYc
Please feel free to post any questions or requests, hope someone finds this of use. 
Really dug this tutorial set. Thank you for making this and sharing. I envy your UV map savvy.
Thanks a lot, wish I could claim some sort of secret, but truth is, it’s “donkey work”. Trying something, seeing how the uv map looks, setting edge seams, try again. The big issue with the mask bit was the sticky-out bits which weren’t on the edge. The key thing I try to hold to is the “unfolded paper” idea, so look for areas that can make sense as a “surface”. Also, as tempting as it is, sometimes, it’s better not to “make quads” on a UV island as it affects how the final texture looks. With this, I found, looking in the UV window, there were clear places adding seams made sense. Until recently, I tried to all seam marking in the 3d viewport, but really, I’d say the UV window was even more important when refining.
Have an add-on export substance Painter, and make a live link ?