I would kill for rocks with that kind of texture and detail.
Personally, I would actually prefer the main rock to be bigger, you could also try to tilt the main rock so that it exerts a bigger personality over its smaller counterparts. This would also create a tension when the scape is viewed, something like, "the rock is gonna fall!" kind of feeling. This tension is essential to Iwagumi scapes.
You would also properly need to keep your foreground plants low, especially on your awesome right foreground. That empty space there between the two rock formations is going to look so good when filled. And to contrast this space further, plants that are taller behind your extreme right rock is gonna frame that entire area nicely.
I do not think you want this tank to be a strict Iwagumi tank, but if you do (it will be a little boring! haha.) then I suggest getting another sharper, taller rock to be placed behind the current big rock. That will add depth to your focal point, which is the main rock. The current big rock which would be then in front of your main rock will add a powerful base to tie your main rock to the entire scape.
I would also highly recommend Eheim 2213 to be your filter. I run this on my Mini M and its simply awesome. You can use Eheim's double tap to control the flow rate if you need to, and when the flow rate slows down because the media is slightly clogged, just open it full throttle! That means longer filter cleaning intervals which I think will appeal to you. *wink*
Okay, sorry for this long post, I had no idea how I rambled on....
Looking forward to this scape!