For the moment, I don't draw any rivers and lakes because I need to have mountain to do lakes and rivers. And before including mountain and trees, I want to color the background on my islands. Perhaps, it's not the good way to progress on my map ?

I use GIMP to make my map.
For the colors : Brown (mountain), Red, (tray), Green (forest and swamp), Blue on island (toundra), White (iceland), yellow (desert and savannah). But the color you is just a random color to symbolize where I want to put the land. Not the final color.

I attached a new map on my first post without any color. My "final" map is only that for the moment.

Zach, I'm not sure I understand what you said here : "Second, clusters of uniform, evenly spaced islands are pretty rare. I'm trying to envision what the land would look like without the sea there, and it looks like a bunch of mesas, of equal size and spacing, sticking up from the seafloor." (english is not my born language) For you, my islands are too tidy ? It's because the size of the picture perhaps. I needed to pu in order each island to put them on the map.
I don't had imagined the seafloor except beetween the two biggest islands. You have a lot of volcanus activity on this part of the sea and at this latitude.