I know you have not "looked at a ton of this stuff", because you don't even understand the basic model that you could see in a 10 minute video. I will address your points. None of these points are related to proofs about flat earth though. You are thinking about it from the wrong angle. You are thinking it can't possibly be true because of the coverup required. It is much better to start with proofs involving flat water over large distances and then later work on the how and the why of the coverup. Again, it is clear that you have yet to consult the resources that I have linked to you multiple times because you keep asking very basic questions.

Where does a flat Earth begin and/or end? If it's flat and finite then it must start and end somewhere. is it a circle? A square?

The shape of what we (the public) are aware of is a circle. It is ringed by Antarctica. What is deep past the edge of Antarctica we do not know.

How thick is this flat Earth? We've drilled pretty deep down so it has to be deep, right? What's underneath it?

Actually, we have not drilled that far down. I believe the deepest reported in somewhere around 8 miles. How can we know what is past that?

How can you explain the Coriolis Effect? That's observable from Hurricanes, or even your toilet.

The below is copy paste. A proper discussion on this specific point requires more:

The “Coriolis Effect” is often said to cause sinks and toilet bowls in the Northern Hemisphere to drain spinning in one direction while in the Southern Hemisphere causing them to spin the opposite way, thus providing proof of the spinning ball-Earth. Once again, however, just like Foucault’s Pendulums spinning either which way, sinks and toilets in the Northern and Southern Hemispheres do not consistently spin in any one direction! Sinks and toilets in the very same household are often found to spin opposite directions, depending entirely upon the shape of the basin and the angle of the water’s entry, not the supposed rotation of the Earth.

“While the premise makes sense - that the earth’s eastward spin would cause the water in a toilet bowl to spin as well - in reality, the force and speed at which the water enters and leaves the receptacle is much too great to be influenced by something as miniscule as a single, 360-degree turn over the span of a day. When all is said and done, the Coriolis effect plays no larger role in toilet flushes than it does in the revolution of CDs in your stereo. The things that really determine the direction in which water leaves your toilet or sink are the shape of the bowl and the angle at which the liquid initially enters that bowl.” -Jennifer Horton, “Does the Rotation of the Earth Affect Toilets and Baseball Games?” Science.HowStuffWorks.com

The Coriolis Effect is also said to affect bullet trajectories and weather patterns as well, supposedly causing most storms in the Northern Hemisphere to rotate counter-clockwise, and most storms in the Southern Hemisphere to rotate clockwise, to cause bullets from long range guns to tend towards the right of the target in the Northern Hemisphere and to the left in the Southern Hemisphere. Again, however, the same problems remain. Not every bullet and not every storm consistently displays the behavior and therefore cannot reasonably be used as proof of anything. What about the precision of the sight aperture, human error, and wind? What about Michelson-Morley-Gale’s proven motion of the aether’s potential effect? Why does the Coriolis Effect affect most storms but not all? If some storms rotate clockwise in the North and counter-clockwise in the South, how do those storms escape the Coriolis force? And if the entire Earth’s spin is uniform, why should the two hemispheres be affected any differently? Coriolis’s Effect and Foucault’s Pendulum are both said to prove the Earth moves beneath our feet, but in reality only prove how easy it can be for wolves in sheep’s clothing to pull the wool over our eyes. -The Flat Earth Conspiracy

How can you explain gravity. Everything falls towards the center of Earth (or a specific point within a body, typically the center), which is why it falls down no matter where you are. Where would that center be? Without gravity on a flat Earth, a bullet shot from a gun would theoretically never hit the ground until it escaped this flat Earth.

Gravity does not actually exist. This is a whole topic on its own and I realize this statement can seem outlandish but a careful look at the history of how gravity came to be accepted in the first place is important. The motion you experience can be explained through buoyancy and density. An object in a medium depending on their relative densities will float or sink.

Why are we the only known, observable flat body? We can use simple telescopes to see other celestial bodies that are spherical and have rotation. Why are we the lone exception?

You are assuming there are other "celestial bodies".

Lastly, for what purpose would people have for hiding knowledge this flat Earth? What is to gain? A big April Fools joke? That seems excessive for a prank.

I addressed this in the first paragraph. The evidence for the "why" is not something you can observe with your own eyes (like the flatness of the earth). It is certainly more important than a prank.