Where katas are concerned, you need to work with the space you have available. Naihanchi and sanchin both take up very little space. They can be practiced pretty much anywhere. I say you should choose one to master and one to do whenever you're bored of the other one.
The first weapon taught is the staff or "long stick." The skills and abilities developed through long stick fight training translate very well to medium and short stick fighting. Some variation of a "stick" can be found pretty much anywhere. A four-foot length of dowel is perfect for training with. Again, with practice, you can use it in a very small space.