SuzzyQ

I'm working on a Christmas gift for my DD who has been so-o-o-o great during the past few years. It's a queen size quilt to replace the one she's worn out.
I think I should continue the pattern another 5 or 6 rows on the top and bottom to make it fit the top of the bed - not using the darker fabrics at all. But after that?
Should I add a narrow border to frame it and if so should it be dark or light?
Can I just add a border measuring a 10 - 12 inch drop all round?
The first picture is just the centre medallion; the second is showing how it looks with other fabrics. The fabric on the bottom right I purchased for borders but I'm thinking it should be the backing? I would need another 2 yards/metres I think.
It's being constructed as sort of a quilt as you go because I'm planning on quilting it myself on my DSM which has a throat space of about 6 inches - just straight lines emphasizing the expanding from the centre. Or should I splurge on a long armer?