I have been using Arca Swiss F6x9 with P45 since May and I have been pleased with my choices. I have 35, 47, 90 and 210 mm Schneider Digitar lenes.
To answer your questions and to add some of my commnets regarding the combination use:
1. You need to get H type mounting plate from an Arca dealer. Badger Graphic Sales is a good place to get Arca stuffs and digital lenses, both Schneider and Rodenstock.
2. Pro for a sliding back is its convenience. You don't have to put ground glass for focusing and remove then mount the back for a shot. Cons for it are a) it is expensive, it is large and heavy. Unless you shoot mostly indoor, the weight and the volume of camera gears should be considered. Since I do mostly landscape shooting, I don't need extra 3# of weight and increased volume of my back pack.
3. A sliding stitching back is even more expensive than a regular sliding back. You should also notice that with a view camera like Arca Swiss, it take 2 seconds to shift the back by rotating a thumb screw. Also, it is not true when some say stitching can be made simply by aligning them in PS. Even Schneider Digitar has small 'pin cushion'effect that requires some size transformation within PS, and its wide angle lenses have noticeable corner drop off.
4. I bought my Arca brand new, and I found its ground glass does not focus perfectly. I believe the fresnel lens, in front of ground glass, introduce an error. I haven't got a satisfactory answer from Arca Swiss. However, I found a replacement focusing screen made by Maxwell Precision Optics (firstname.lastname@example.org
), and found it exceptionally good. A bright screen with small grains, and tack sharp focusing.
5. You don't need any additional bellow (other than the one come with the camera) since it function well for all my lenses, from 35 to 210 mm
I hope this help.