draw out the space on some graph paper.

at first glance, I would put the vanity/sinks in front of the windows.

Yes, you can hang a mirror in front of a window.

Can you move the door into the closet such that access to the closet is directly from the bedroom, thus recapturing the vestibule space for the shower? What is the space between the toilet and shower? A linen closet? Do you need that? If you captured that space into the shower would that be a large enough shower for what you want? Can you flip the positions of the shower and vanity to achieve your goals? A freestanding tub needs about 12" around it so you can get around it to clean easily. Which size tub are you hoping to be able to use?

Can you redraw the space on graph paper so we can determine exact measurements? Include the bedroom and closet so we can see how all the spaces go together. Without exact measurements we are shooting in the dark.