Yes, a backing fabric makes a big difference for really smooth, nice looking embroidery. I just use very thin muslin. Whatever you choose be sure it needles well (something without a tight weave). I take a favourite embroidery needle with me to the fabric store when buying more muslin and just run it a few times in and out of the fabric to be sure it needles well. Be sure to baste. I like
Sharon Schamber's quilt basting method because it works well for both hoop and hoopless. For embroidery I baste closer than she does.
Using an embroidery hoop or going hoopless is personal preference - I decide project by project. But if you try hoopless and find you're still getting bunching, then a cheap hoop might make a big difference for you.
If you don't want to use a base fabric, then you must use an embroidery hoop. Be sure to get one that fits well in your hand. A small one that needs to be shifted to a new area more frequently is much better than one that is too big and will strain your hands.
Crochet thread vs floss is just personal preference on the 'look' they give. Just keep in mind that a thicker thread will need a needle with a larger eye, to prevent shredding.
It's tempting to pull stitches tight but resist it, that will create bunching/puckering. Even when using a hoop, if you pull too tight you'll get bunching when you take it out of the hoop. Keep an even tension.
Very pretty block, by the way!! Love it
