This is a huge room! The biggest thing I see taking up that space is that for your list of needs you have 3 different tables- vanity, sewing surface, and possible computer desk. To minimize that, look into a foldaway table that you put up on the wall so you can take it down for sewing and put back up. That along with a spool shelf and shelves with clear containers on the wall opposite your closet (Look up DreamBox or ultimate sewing box for examples) will solve those needs. You should still have room on that wall for a computer desk as well.
Depending on how the window is shaped, I think you could put cube storage on the wall under the window and have a window seat on top.
I would put the full length mirror on the wall next to the window beside the closet, so you could use a full 3’ wide mirror if you wanted and have space to decorate around it. The next bit is hard to explain but I’ll do my best. I would make a fake wall by putting a room divider at a right angle to the wall with the mirror on it. Put some hooks or a shoe rack on the wall space between the bathroom and closet and you have a luxe changing area.
On the other side of the partition or room divider I would put the vanity, and a cute rug with a small plush chair so you have the rug for beside the window seat and the vanity, without blocking the cube storage.
Then you have all the space on the wall opposite the window to decorate however you like! Sorry for the long post, I just wish I had a room this large to work with!