One question: does the bed have to come off the window wall?

Yes - there are French doors , a fireplace and closets on other walls

You can stay with bedding the color of the bed/frame and then use one of the bolder colors in the art for bed accents.

The bedside tables make everything look so crowded. Any other spot for them in the room...either side of fireplace?

No there really isn’t another spot

That looks great! I was thinking of a sage green or rose colour but I like the beige. My duvet cover is actually gray and am replacing it ? Maybe more beige?

For the quilt I'd stick with a white, cream or very light beige quilt, but the shams and pillows you can pick out any color from the painting. If you're one that likes to change things up, changing out pillows from time to time would be an easy and relatively inexpensive way to do that.

Here's a quilt that I love:

https://www.amazon.com/dp/B0CMQGPRTX?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_6&th=1

Very nice!!

Sage green could work beautifully here, but I would use it as an accent rather than across the entire duvet. A warm ivory, soft cream, or light oatmeal duvet would give the painting some breathing room, while sage green and muted rose pillows and a throw would bring in the colour you’re looking for. For the upholstered bench, a warm taupe or camel fabric could help tie the bed, artwork, and new bedding together without making the room feel too busy.

I recently put together three complete bedroom design schemes showing how bedding, furniture, feature walls, and layered lighting can work together to make a bedroom feel more polished and expensive. You may find a few useful ideas for finishing your room here: https://youtu.be/nEcPGozCbFY