Help with continental features

I am having enormous fun creating tiled worlds! I was wondering if I could get some advice on finessing my continent and if there are better ways to do what I am trying to do!
I am trying to control where geological features would appear so have experimented with sand dunes, hills, cliffs and mountains.
Basically I would like a slightly more raised continental shelf, (So it doesn’t just disappear into the sea) Some of the individual islands are suffering from this where they are basically just a series of ridges jutting out of the sea rather than a solid island. Part of the issue I think is it’s the way I have used an inverted version of my continent to show where the sea goes.
Secondly I wanted to make some sheer cliffs, but I have ended up with more of a featureless line. Any advice or macros that would help would be much appreciated!
Also I could really do with flattening the seabed (I am hoping to take a future continent of mine into Unity and the less obstructions I have on the sea floor the better!)
I have also been experimenting with “choosing” based on other forum posts I have seen and think perhaps I could bring the different geological sections together better.
Any other thoughts on improving geological features would be great too. I want to really get the best out of this and know I am only at the beginning of the journey.
I have attached my world below!