I guess the diameter of the rod might depend on the weight of the quilt. A heavy quilt might bend a thinner rod? I've never hung a quilt, so I'm not sure. Just make sure the hanging sleeve on the quilt is big enough to accommodate whatever size rod you use.

Yes, it all depends on the weight of the quilt.

Considering the size of the quilt, I would get the 1 inch. You can also find the ones with the decorative balls on the end. They look pretty nice. :)

Also remember that a lot of the ones you extend will want a brace in the middle as well as on the two ends. So, a thicker rod will be more likely to hold the weight without that center support, unless you do a tab top hanging set up like on curtains.

I can't wait to see this quilt you keep talking about!

If the width requires a brace in the middle, put on a split sleeve (two sleeves with a space in between them) and you'll have room for the brace. The standard for show quilts of all sizes is a 4" sleeve and many are hung from 2" wooden closet poles, so your 1" rod is as small as you should probably go.