Well, I did it.
It turned up to be quite a journey from making both the Japanese curry powder and making up some fresh garam masala to making the Japanese Curry Roux to making the katsu curry today. There are a couple things that I would change like cutting the vegetables bigger and perhaps the next time I won't let the roux get quite as dark as I did before I add the spices. Other than that it was delicious and I would recommend the recipe to anyone.
And the really great thing is that I have enough roux for three more meals.