Exactly. You prove my point.
Of course not. You're going to veer northwest. On a sphere you can travel purely west. On a flat circle it will be northwest. It's still a westward direction. This is too simple to argue. Draw a circle on the goddamn floor, follow the outline of the circle and you end up in the same fucking place you started.
Light spreads, which means it's less concentrated, therefore less intense.
"The Law states that the intensity of a source decreases at a ratio inversely proportional to the square of the distance it travels. Basically this means, as the distance doubles, the light intensity decreases by a factor of 4." -
https://www.parabolixlight.com/debunking-the-inverse-square-law
The sun in the globe model is omnidirectional, therefore the inverse square law applies. The light would be too dim for us to see Saturn.
Here's a whole presentation on it: