That's a pretty short bellows draw for a 7x17. You might get a longer bellows made (won't cost much more) with the goal of eventually making an extension track for your 7x17 Agfa.
As far as 12" lenses go, the 305mm G Claron would be a good choice for 7x17.
I had my bellows made by Camera Bellows in England. While I would not call their products cheap, they are extremely well made and offer an excellent value for the money. One nice thing about their bellows is how small they collapse. I needed my bellows to fold down fairly small when the camera is collapsed for transport. I told them I needed at least 27" of extension, but would prefer 30" and it needed to collapse down to at most 2" for transport, and 1½" - 1¾" would be better. They exceeded my wildest dreams - they made me a bellows with 30" of maximum extension that collapses down to an amazing ¾". This deluxe bellows cost about $350 (200 British Pounds) and is worth every penny (pence).
Kerry