There are all sorts of products out there for managing spools. I'm fond of a product called Hugo's Amazing Tape - it's plastic that is stretchy and self-adhering but not actually sticky. Sort of like Saran Wrap, but much thicker and on a roll like tape. I wrap my spools in a length of that stuff and they stay nice and contained. It's not cheap but it's endlessly reusable.
What to do with your embroidery? All sorts of things! If you're going to embroider on quilt-weight fabric, look for less dense designs; otherwise you have to add stabilizer and that can change the feel of the quilt. I've embroidered fairies and monkeys onto quilt blocks for boy and girl baby quilts. I've embroidered herbs onto kitchen towels as Christmas gifts. I've embroidered names onto the cuffs of handmade pillowcases. I embroidered old stereos onto patches that I made into hot-cup cuffs for my DH. And that's just barely scratching the surface of what you can do...
You can get patterns for "free standing lace" where you embroider onto wash-away stabilizer - then you wash away the stabilizer and you're left with a lace doohickey - maybe it's a coaster, maybe it's a Christmas ornament, maybe it's a lace cuff for a shirtsleeve....so many crafts and ideas are out there!