Congratulations on your purchase of the 12X20 Folmer and Schwing. And welcome to the fascinating but sometimes baffling world of ULF!
Bellows draw on an unmodified Korona 12X20 is about 24", slightly less on a F&S. 12X20 F&S cameras were made on a single extension rail that allowed only about 22" of bellows draw. I have heard that a rear extension rail was available for the F&S but it must have been very rare because I have never known a 12X20 F&S owner that had one. This means that you won't be able to use your 24" Artar without some kind of front extension.
Most people who use the F&S camera simply adjust their type of photography to the limiations of the camera by using wide-angle lenses, and for a format of this size anything less than 24"-26" would be considered wide-angle.
The 12X20 F&S was well-made and many remain in good operating condition in spite of their considerable age . One of the features that added erxtra ridigidy to the design was the non-removable back. The camera should have both swing and tilt on the rear, front rise and fall, and front tilt by means of a separate front bellows. Ther is no swing on the front unless the camera has been modified.
A short list of lenses that will work with this camera with the 22" bellows limitation follow.
Schneider 210mm SSXL
Goerz Dagor 14", 16.5", 19" (but not the 14" Gold Dot Kern Dagor)
(some older 12" Dagors will also cover stopped down to f/45 or f/64 but performance at the corners is marginal)
Goerz 19" Artar
355mm Schneider Symmar (convertible type)
For just one lens it is hard to beat the 450mm Nikkor-M for coverage, size, performance and price.