Some of your problems are coming from a contradiction. If you want realism, you cannot have a floating volcano, period. Volcanoes come from deep in the mantle or deeper.

If you want total fantasy, then you don't care about any of the geology, tectonics, geography, realistic climate zones, etc.

You really can't have both. I think you should decide if you are just going to place land features wherever you want them, or if you are going to try and make your world look real. Once you have decided that, it will be much easier to make decisions about placement, terrain features, biomes, and the rest.