I have the same boat.
1. Swingback seat is not ideal but it works. You can easily slide a 48qt cooler in from the front but it's a pia to get into I typically bring a 30qt which slides in and out easily. I have seen custom leaning post with tackle storage and rocket launcher installed on the 180.
2. Mine has the freshwater shower installed, tank is under center console, pump is under port aft seat, shower hose is in port aft gunwale. Nice to have but I haven't used it in years. For raw water you would need to drill thru hull for intake, install sea valve and run tubing and wiring for pump. 5 gallon bucket works fine.
3. Forward fish box works great. Depending on planned trip length I'll buy anywhere from 20-40lbs of ice and it lasts just fine. I'm in the northeast so it's rarely 90+ degrees might be different down south.
I love the boat for what it is, it's small, seaworthy and easy to handle. But it's small and any projects are difficult because everything is hard to access. For example the grab rail on the stbd side of center console was loosening up, try getting inside the console and getting a wrench on the nut, very difficult. Same with swapping out bilge pump.
Good luck!