For what you've described, an 8 ft 5 wt rod is the best compromise of casting distance and ease of use in tight streams. Ideally, a 7-7.5 ft 4 wt would be ideal for a small, tight stream. And an 8.5-9 ft 6 wt would be perfect for pond and lake fishing. So split the difference, and you get an 8 ft 5 wt.
Only you can decide whether to get a 2, 3, or 4 piece rod. Are you honestly going to backpack long distances with it? I regularly hike several miles with my 7.5 ft 4 wt put together and rigged up already, including with the line though the guides and a fly on. I occassionally will pull it apart and carry it, but most of the time, I just leave it together. Unless you're planning on going on long hikes to get to your fishing holes, or frequently backpack with fishing gear, get a 2 piece. The St Croix Premier would be my choice. The P805.2 is the 2 piece model ($80 list, but can be had for $50-60 on eBay), and the P805.4 is the 4 piece model ($100 list, and harder to find a deal on).
As for casting differences with more pieces, in a good quality rod like a St Croix, and with your limited experience, you're hardly going to feel any difference at all.