Hello, brutaldelux.
I see you are interested in finding the truth through evidence. I think I can help you with some of that.
First off, I wanna state that the existence of a God is independant of the Earth being Flat or round. In both cases, he could and could not exist.
So, let's look at some visual and pratical evidence, shall we? We can easily confirm that:
The Sun appears to go through the sky from West to East, and so does the starts at night. Both maintain, throughout the day and night, the same shape, size and relative distance. At around 6 PM, the sun "sets", it goes below the Horizon, sinking, but still maintaing shape and size.
More visual evidence: at different parts of the world, it could be night or day. For example, while in the US is day, you can easily communicate to someone, at the same time, in Europe, and the will claim it is around night, where the sun is not in the sky.
Whenever we drop an object at a great height, we can observe that it accelerates towards the ground.
The moon affects the tides, growing bigger or smaller depending on how the moon presents itself. Also about the moon, it seems to dissapear under some kind of shadow at some times of the month.
When we see a ship sailing away, we notice that at some point, it starts disappearing not in a blur, but bottom first in the Horizon. But, when we go to a very high point, we can see the ship more clearly again.
I want You, in your deducive capablities, to make sense of all these facts that we can easily observe everyday. Now, this is a path I consider you to thread alone for now, in order not to get too attached to any particular theory. Come back once you get some conclusions to show us.