The "platform" actually doubles as the chicken door. Here's a photo of it closed, for reference:Nice...kind of steep tho, throw a few more blocks under the low end.
All that stuff on the platform is not needed(I don't think).
The bottom square thing isn't super strong, and could benefit from a diagonal brace below, but it's ok for now and I don't want to install one until we (finally, haha) get the coop painted.
if you really think it needs bracing both inside and out, I'd replace the triangle pieces with a solid piece of plywood. Those chickens are going to poop on the open door and having it all "trapped" in the door will make it really hard to clean.