The 8" blade will hold 50 ml of emulsion. This is enough to coat a carbon sheet with a huge laydown. I forget the entire amount. I think it is close to a 100 mil gap.
I have coated up to 13" wide, but with lots of defects with a 5 and 7 mil gap. I have coated 11" with few defects, so I'm having the 13" blade resurfaced and re-leveled to eliminate some problems I found during testing. I have a 16" blade but have not tested it yet due to time constraints.
As for length of coating, that is limited only to your reach. I can coat longer than 12" as is, but standing on a stool and extending my reach I can coat over 20" or more. If the paper is moved continuously, and the solution is added, this will coat any desired length of paper or film that you can handle. After all, a similar method was used originally to manufacture film and paper.
The blades are being sold at cost plus a pro-rated amount for prototypes at the present time. I will publish the drawings when I recover the cost of the blades currently made plus the development costs. Then I will exit this business and leave it to the moguls.
I made about 20 blades for my classes and to sell (10 for each). I have about 7 prototypes including the film and plate blades which are of a different design. So, it is a total of about 27 blades cost divided up into 20 blades. Each blade has about 1/7 the amount of development included in the cost.
I cover this and demonstrate much of it in the workshop. After all, part of emulsion making is the ability to get high quality coatings. If you want to, you can always use a brush or spray gun.