Yeah, it is tricky to find a balance between blocking unwanted light and not making it look like your store is closed by covering up a window with blinds or a too-dark curtain. A quilt sounds like it could be a good compromise--I bet you could even position it strategically so that it blocks the sun during most of the day but still doesn't cover the whole window, and put some other sewing- and quilted-related things in there to fill up the space.
Great that you found a POS system! That will make things a lot easier for you, and definitely help over having price tags and a calculator like some small shops. You'll have a nice professional look rather than a garage-sale feel.
Will you accept credit cards? That really made a big difference with my sister's store. Now of course you can even accept credit cards with your smartphone and one of those free Square readers. (That's what my nephew uses at his bike shop; he was just telling me about it the other day. 2.75% per swipe and no other fees. Great for a new business like his, or yours.)
From the photos it looks like your biggest task in the weeks ahead will be filling your shelves with inventory. That's always hard. My sister once bought two thousand dollars of cards that she was only able to finally sell two years later at half the price she paid for them. She called them "the bane of her existence." After that, she never bought more than $500 or so of any one thing that she hadn't already been selling, and even found a couple of suppliers where she could return unsold inventory within 90 days, which really helped.
~ Miss Fleecy