I haven't read this thread, but you missed a very important part of the global flood, and that is those mountains didn't exist as they are now, the flood created them. They were mountains but the flood itself raised them much higher. This is why ocean-bottom sediments, full of marine fossils can be found on the highest mountains. Mt. Everest itself has clam fossils at its summit.
Psalm 104:8
The mountains rose, the valleys sank down to the place that you appointed for them.
While the mountains rose higher the oceans got much deeper. The world was much more even pre flood.
We also know that part of the flood water was water from under the earth, it came up as 'fountains of the deep.' That water or some of it went back again, its under the surface.
Genesis 7:11
In the six hundredth year of Noah’s life, on the seventeenth day of the second month—on that day all the springs of the great deep burst forth, and the floodgates of the heavens were opened.
Then as for the water on the earth, some is frozen. Antarctica is covered with ice on average 2,133 meters thick. If all of the Antarctic ice melted, sea levels around the world would rise about 61 meters. The rest is in the oceans and below the surface of the earth.