With regard to your second question about whether the step up ring would affect picture quality, the answer is that it shouldn't.
- You are putting a larger filter on a smaller lens so it won't obscure the lens in any way.
- The quality of the 58mm filter will be the same as a 49mm filter (assuming the same manufacturer etc.)
If you leave the step up ring attached then there's no effective difference between this and having the correct sized filters. The only advantage of the 49mm filters I can think of is that it would look "cleaner" (but hardly worth the extra cost).