Whatever you do for shoes, just be sure you don't buy them only a few days before your big ride. You need to be sure whatever shoes you wear for 40 or 80 miles are going to be comfortable. Try the new shoes out ahead of time on a couple long rides, and also bring a SPARE pair of comfy shoes you can switch to if the new shoes give you pain after lots of miles.
Same for the padded shorts- if I were you I'd bring two different kinds just in case.
Tops? ...whatever is logical for the temperatures, plus the sun and rain factors. Try to have several thinner, breathable layers as opposed to being stuck with just one thick layer. That way you can regulate your body temperature better by adding/removing a thin item or two. I often wear a sports bra, then a breathable tank top, then a lightweight longsleeve top. As I heat up or the day heats up I just take off the outer longsleeve top. Another choice is to have a lightweight wind vest over a light longsleeve or shortsleeve top- then remove the vest if you get warm.
I myself use a bike saddlebag and am not into stuffing things into a pocket on my back. Others like the back pockets of jerseys.
Remember to use your sunscreen! Sunglasses help too. Doesn't hurt to bring a very lightweight windbreaker/rain-resistant jacket or vest. TWO water bottles if possible.
Sounds like you're going to have FUN!