You have a lot of space and no one else will claim it, not at least until you clean, insulate and finish it J
Don’t rush with layout plan, it will evolve and take time. Ensure you have room for turnout motors should you decide to install them later.
What I did first is settled on benchwork / framing plan that was driven mainly by the room size. I could not work on benchwork after 9pm due to noise so I had to switch focus and had plenty of time to think about layout plan. It took me almost 2 years to build benchwork and during that time my layout plan kept evolving.
When you plan for benchwork - make sure the height is right for you so you don’t have to bend your back to operate layout and all major areas have easy access (2’ is good, 3’ max). That is perhaps even more important than layout plan for enjoyable construction process, layout operation and will be difficult to change later.
Given that you’ll likely have temperature/humidity swings in your room – keep in mind your benchwork with shrink/expand during the year. Curved track is bit more forgiving for dimensional changes than straight track, so that is something to keep in mind when you design your plan.
Slava