There are specific times that guest are allowed to pay for the fish.. to feed the dolphins, so make plans accordingly. It is basically based upon the dolphin feed schedule, since once their full they do not eat anymore fish.
The show times are also posted on the SW site and it may be easier to plan in advance once the times are posted. Just remember their subject to change and they may change more than you think too. Remember walking time to traverse the park and arrive 30 minutes or greater to have the option of choosing where you want to sit.
I like to sit in the splash zones to fully experience the excitement and I would recommend bringing or buying a poncho if you elect to do this and bring some form of water protection for your camera too.
Happy Harbor and Water Works are very popular with kids and there are a series of areas where kids can get wet too. I also remember a blow-up bounce attraction which was very popular with our youngest.
As far as SW crowds go...you really do not need to worry about crowds like you do at Disney World. Overall, it is always best to avoid the weekends as the local season pass holders will frequent during the weekends. We have normally visited SW prior to Disney and normally visited mid-week. SW is a relaxing environment once you formulate a show game plan...enjoy your trip.