Help, Starting on my first track plan

I would go with around the walls and 30 to 36" wide with hammerhead ends to allow looping around.

Alternately, make a lift up or drop down gate for the entryway to allow full looping around the walls. You still want a way to reverse from both directions somewhere if possible.

It depends on how tall you are, the height of your layout, and what you are trying to do with that portion pf the layout.  The diameter of your curves will also be a factor.

My around the room layout has shelves that a 2' and 3' wide with a 4' wide peninsula in the center.  Two feet is enough room for 4 parallel tracks.  The operating/viewing aisle is 3' wide while the maintenance aisle on the other side of the peninsula is 2' wide.

If all you want to do is close the loop with a single track then you can go as narrow as 6".  I've added triangle pieces to the inside layout corners that allows me to use larger radius.

One thing to remember is by keeping you track not parallel to the edge and putting a slight curve in it is pleasing to the eye.

Jan