I've used Diafine and HC-110 (Dilution H or G) for Fomapan 100 in 9x12 cm. I can't imagine Rodinal or R09 being bad, however; the grain with dilute HC-110 is almost invisible in 2400 ppi scans, and the tonality and acutance are up to anything the lens can deliver.
I think you're going to love your Ideal, but if you don't, let me make an offer if you decide to get rid of it. I'd love to have another working one and more plate holders.
One thing I do recommend with Fomapan: if you use a development method that has the film in contact with a surface, you'll need to finish the wash after removing the film to a tray or tank in which the back side can wash; otherwise, you may find splotches of antihalation dye that failed to wash out and produce light areas in prints. Ideally, you should wash in an alkaline bath after removing the negative from the tube (this really applies mainly to tubes) immediately after fixing, then do a full Ilford method wash with the negative accessible to the wash water on both surfaces.
Attached is a tiny crop (1:1 at 2400 ppi, just over 5 mm square) from a test negative made with my Ideal and 13.5 cm f/4.5 Tessar -- this was shot at EI 160 from about five feet distance, and I hadn't even noticed the nail in the stump; development was in Diafine. HC-110 give slightly finer grain and a little more contrast; dilute Rodinal should give better contrast and about the same grain.