Apologies for responding late; I do not get notifications on this site whatsoever
According to the requirements, YOU get to design/sketch the menu from top to bottom. If you think this sort of menu can somehow fit on one single page, then go ahead and sketch it as such. Be warned; I will judge you harshly for all your sketch decisions. If you sketch a menu that is hard to work with, doesn't allow for new features, etc. it will just count against you. The dimensions don't matter. The first input should be keyboard and mouse since this is a native desktop game, however, its recommended to sketch/plan around ALL platforms. Even VR.
If you're concerned about payment, you can use the Upwork link provided to accept an official contract and I can respond faster with better details and such.
Thanks