I though as much. I am redrawing the plates to be smaller and will combine A2 and C to a degree. When you say "continental seas" do mean when a tectonic plate that contains both land and a significant portion of an ocean?
I am going to have to work on the plates involved with the major continent first. Many of the islands you see have not been dealt with, and they are supposed to be volcanic in origin (as you might have guessed). I will consider what you and Hawksguard have said and repost a new map tomorrow. I just got home and have to be back at work in less than 7 hours. Keeping the major plates in place but breaking them down into smaller components might be the best alternative.
In regards to the barriers you mentioned. The area south of the mountains on the northern reaches of D is an expansive savannah and large portion that resembles the Kalahari desert. it's already a formidable barrier. I am not so concerned with how impassable the mountains are just as long as they create a rain shadow.
EDIT: I forgot to thank you for your help. Thanks.