One is always concerned with the image circle when using movements. Think of a piece of paper taped to the wall across the room and you standing on the other side of the room shining a flash light at the paper. If you point the flash light right at the paper, you can easily illuminate the whole sheet. Now...imagine moving either the paper, the flashlight or both. It's easy to see that the paper might easily fall in darkness. The paper is your film and the flashlight is your lens. Make sense? As you move the flashlight closer to the paper, the circle of light is casts on the wall gets smaller too....well, it does if you can kinda focus the beam of the flash light - like with a Maglite.
That's one of the problems with movements in general - does the lens project a big enough image to allow this much movement?
The other has to do with the geometry of your camera and its bellows. Shorter focal length lenses focus closer to the film plane - they want to be closer to to the film - they squish up the bellows. If you go too short the bellows may not squish up enough to allow the lens to get close enough to the film to pull focus...and even if it does, it may be that the bellows is so scrunched up that it is really hard to move the lens with respect to the film plane...or, some other part of the camera may bump into somebody else...some cameras just don't like those short lenses....the shorter you go the more trouble they are.
All this is much easier to do than to think about. Once you have a lens and have tried it out a few times...you laugh that you were ever concerned about these things. It is much easier to learn by doing - at least it always seems to be for me...try to find somebody local that can help you the first time or two - if even for only an hour. It'll make it all much easier.
Where are you located? If in the S.F. Bay area, I'd be happy to help.