It's turtles, all the way down!
Really though, FET probably would conjecture that it's just dirt or rocks or whatnot. And yes, if you went in a straight line long enough you would fly right to the edge of the world and see the icewall, beyond which is a vast wasteland of frozen tundra and harsh weather conditions that the sun's distant light cannot penetrate. There is some debate whether you'd go over the edge, or whether it extends to infinity.
Problem is, there are a lot of things that either prevent you from getting there, or which prevent you from rendering acceptable evidence of your journey. Among them are:
-Light bends, so you may become incapable of determining your direction of travel and end up back at on one of the standard continents.
-GPS tracking data might contain algorithms which cause GPS units to display the appearance of a round Earth, when really it is flat. This misdirection would probably lead you away from the icewall and back to land.
-The Conspiracy may have set up watchposts or patrols around the near perimeter of the icewall, to prevent wayward explorers from discovering the Truth and returning with evidence to civilization.
Time zones are pretty straightforward; the Sun on a Flat Earth is generally proposed to be something like a spotlight that moves around the sky, illuminating different areas of the Earth at different times. To my knowledge, this position still has issues with matching the light output from a spotlight to the predicted (and well-documented) daylight patterns that exist around the world.
Gravity works in one of two ways. The infinite plane Earth holds that gravity works similar to how round Earthers think it does, meaning that matter attracts matter or bends space-time, etc.; the finite thickness and density but infinite expanse of the Earth is theorized to account for the gravitational effects we feel.
The other option is Universal Acceleration, which is a whole other can of worms. Essentially, everything in the universe is accelerated upward at a constant ~9.8 m/s^2, but the Earth shields us from those effects so we feel that acceleration towards the Earth (or that acceleration of the Earth towards us) and experience gravity.
And I don't know what's up with wind? You're going to have to be more specific, I don't see why a flat Earth can't have high- and low-pressure atmospheric conditions to create wind.