Well, as for water...hydrogen and oxygen are two of the most common elements in the universe, with water being one of the most common molecules.
As the planet cooled, it allowed new types of molecules to form, water being one of them. Plus with a lot of the volcanic activity at the time there was a lot of outgassing of water vapour, or at least hydrogen and oxygen. Also, there have been billions of asteroid impacts to the planet and a pretty big chunk of them were most likely ice asteroids which added to the total water content.
As for the landmasses, since earth is volcanic the "land" is actually floating on a sea of magma. The current theory is that all the land was part of one super contentent million of years ago called Pangaea. Over the billions of years since, each part of that super continent were on different continental "plates". As the plates move around the magma they take the land with them. Mountain ranges are formed where the plates crash together. Islands form from coral in shallow water or from volcanos in deep water.
Erosion probably plays a big part in the fact that you don't see as many islands on earth as in this venus map, however, Earth has a LOT of water. If the levels of water dropped you would see a lot more islands, and if they raised you would see a lot less land period.
Over a few million years after the terraformation of Venus, a lot of those little islands would probably be reduced to rocky highplaces under the water.
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