Best to fill the bladders just before going to the water. Changes in temperature can cause pressure changes in the bladders. Warm air to cold water can make bladders soft. Full bladders left in a warm vehicle may expand and rupture. There is a chance you have a leak in your bladders if they went down a lot. There is some history of the welded seams leaking in Fish Cat 4s. Fill the tube at your house and let it stand at a constant temperature for a few hours to see if you have a leak.
Anchors....tie a rope from one side of the boat (off plastic D rings), around behind the seat, and then tie off on the other side. Make it slack enough so that the this rope can stretch back near to the point. Now you can tie off an anchor rope to this rope (I also tie my net off to this rope). I use an 8lb rubberized dumb-bell weight from Walmart. Get some 1/4-5/16" cord for your anchor line (can wrap it around the dumbbell). I tied single knots in the line at 5 ft marks to give me an idea of water depth.
Flippers...go to a dive shop and get some diving fins that slip over your sock foot waders. They move way more water and you can go way faster than with force fins or other fins used over boots.
There will be some water(couple of inches) in the back compartment. I have a wet bag the size of a sleeping bag that I store stuff in.