does the coast continue to seep in till the whole map is water, or is there a limit from the starting point to how far the coast will erode?

i want to know that too also does the rate soil is eaten depend on terrain?

There are no limitations in distance.

Currently, erosion tile candidates are chosen from 5% of coast tiles within range from 1 to 100 by randomly on every 1000 ticks.

1 <= 5% of coast tiles <= 100

Theses candidates are tended to erode by depends on its surrounded water tile count.

This means, The tile which surrounded by 3 water tiles has a big probability to be eroded by comparison to the tile which neighbored 1 water tile.

On the other hand, there are no difference in erosion speed with such as grass, sand or something now.

can you make the erosion rate adjustable please?

That's sounds good.
I will try