I wouldn't hesitate to stock up a large quantity of unique films for which there is no substitute, like Konica Infrared in 120 size. However, I don't think APX400 belongs to this category. If I were you, I'd buy enough APX400 to go for another 6 months, and a few rolls of potential substitutes to test out before APX400 exhausts.
I'd suggest the same for Rodinal. People are too pessimistic about the future of b&w photography. I know of a plan of new b&w processing chemicals to be offered for sale by a small but motivated company (Not Fuji, Ilford or Kodak) and I also know that their catalog includes two or more new film developers. So, I wouldn't go crazy in stocking up a huge amount of materials.
(However, I stocked up about a grand worth of AGFA MCC and MCP. I don't know of any other paper that works similarly in my developer-toner combination, and I already started building my portfolio using this combination...)
So, market analysis is one thing, and faith to b&w photography is another thing.