Welcome to the site. I have a 03 3280 RL
We just love it. I have owned it for 2 years and so far have towed it about 26,000 miles. So far my rig has been trouble free except for a controller for the pilot light on the fridge. it was a simple fix. I also got rid of the sewer hose on the front of my rig and installed a bigger one to fit the larger Rhino hose setup. You will need that hose system for the sewer draining. I also have one of those step down hose supports. Here are some links to things you will need.
I got one like this not this particular one but the one under there won't fit the newer hose. Had to improvise my install. I drilled into the bottom wall that hangs down and used some long bolts and covered them with some 1/4 inch copper tube to dress it up. The frame under the rig hangs down from the walls a couple inches. So when you put the tube under there you will have to make up the difference . You will see what i am talking about when you get your setup.
Here is the newer hose I have 2 hoses total length 20 ' I have used both at the same time.
You also need a serge protector. I got this one. Not cheap but it will protect your RV
I also use a pocket hose for my water believe it or not. Some folks may not recommend it but i have only experienced one leak so far and it was minor. They dont take up much space and are easy to handle. If you are going to park it and live in it than I would get the white hose otherwise the pocket hose is the best. I like the 25' ones but cant seem to find them as cheap as they were. Maybe able to order then from the TV. But you can find 50' ones everywhere.
Dont forget the filter for the water hose. I woudn't hook up without one. You can get them at any RV store or order them online from Camping World.
There are many more things to get for your rig including replacing the TV that came with your 5er. LOL
GALLEY TANK DRAIN. Handle is between the rear tires on frame rails Hard to see but it's there. Be careful as last guy may have never drained it like the people that owned mine LOL . I have figured out many things since i have owned my rig.
Remember you have 2 power supplies inside the rv. One is 12 volt and some 110.
A 30 amp service will be fine for your electrical hookup. I only have one A/C unit and 30 amp spaces are cheaper than 50 amp
Have fun RVing.