This may help, it's a list I compiled of feeder nutrition. I don't have the #s yet on the discoids, but they should be in a similar range to the dubias and Turks.
Here's a list of nutritional content:
Insect: (M) moisture, (P)protein, (F)fat
Dubia roaches: (M) 61%, (P) 36%, (F) 7%
Turkistan roaches: (M) 64%, (P) 37%, (F) 5.5%
Lobster and Discoid roaches are in the same range as the dubia and turks.
As far as raising Discoids, someone else may be able to help. I have a dubia colony that is really booming and have been really pretty easy to get started. Much of my info comes from some great people here on the forum. Get in touch with any of them, check out the websites of the roach vendors too:
www.theroachguy.com
www.theroachranch.com
www.afexotics.weebly.com
or check out this thread:
viewtopic.php?f=76&t=116814
Lance (Twobeardieguy) has a lot of good info and pics on this thread.
Good luck on whichever type you choose! Roaches are really the way to go!