Any color will fade (including a permie) if you're swimming a lot. In fact, ALL chemicals (including your texturizer) have the potential to react with the chlorine in the water.
I would just take a lot of precaustions (wetting and conditioning your hair before a swim and using a swim cap).
No Sebastian color will "show up" in the same way as a permanent color - especially if your hair is very dark. You would be able to enhance your natural color (with Neutral Brown like, Allandra, or something darker), as well as go darker (with Brilliant Brown, or Coffee Bean). Some of the reds would also maybe give you some highlights in the right lighting - but it wouldn't be obvious unless your hair is naturally medium or light brown.
I used Textures and Tones for a long time and I never had trouble with excesive dryness. Like any chemical, your hair will feel slightly different after you color for a few days or weeks (it depends a lot on the condition of your hair before you color) but on me, my hair wasn't irreparably dry.
HTH.