I heartily agree with Mark here.
If thew volcano is god powered, it may as well be not affecting the rest of the world, because, you know, god-stuff. I get Chick's point though: why bother with realism if anything goes anyway?
Apart from that discussion my advice would be not to overthink the details of tectonics and geography. I usually go with the flow and outline the continent and put in mountains in what feels right to me. When that's done is when I start going to a bit more detail regarding biomes.
In the end I think it's the story that should mostly dictate what you need where. If you want a desert next to arctic regions come up with a reason for it. If you do not NEED a desert next to an arctic region, put it where it belongs. To get a better grip on the natural placement of biomes I like to just look at google earth.
Hope that helped a little.