I'm skeptical you can order the 32" barrel separately, but the only way to know for sure is to call CZ and ask.
As for 30 or 32" barrels, it 100% comes down to personal preference. Skeet is shot with gauges down to a 410, so a 12 gauge with either a 30 or 32" barrel is plenty sufficient. As for which is better, the answer is it depends on the person. Some people find the 32" barrel smooths out their swing and prevents them from whipping the gun around. Others would tell you that a 30" barrel is the perfect swing speed for them. If the gun swings well for you as is, I would stick with it. If you find you tend to whip it around, I'd look into a longer barrel. That said, the longer you wait, the harder it'll be to swap the gun out, and may already be a bit difficult if you aren't posting this from your FFL's shop.
Let us know how you like the gun though. I had a redhead deluxe 28" for a bit over a year and it performed quite well, so I imagine the sporter model will do quite well for you.
