I also use spray adhesive. Usually the kind made for fabrics is considered safest, but meh. I've always liked krylon but the others are okay too. Don't use repositionable spray as that doesn't hold well. In my experience 505 is more expensive but not any better than krylon.

However, you need a smooth surface to spray baste (at least the way that works the best for me). I lay the backing out and tape it to the floor so it is tight and then add the adhesive-batting-adhesive-top, unfolding the other two layers so they are centred on the backing. That way you don't have wrinkles and you can true the top with the backing. You do need to lay newspaper or similar down on the floor beside the backing to keep the adhesive from covering the floor. And it requires a deft hand--even the best adhesive can be applied too liberally or too lightly. It takes some experience to get just the right amount to hold the quilt together well without causing gumming, clogging or stiffness. I also always wash the quilt after I am finished in hot water with synthrapol, which will take most of the adhesive out nicely.

Depends on the colour. Will the backing colour bleed all over the quilt? Then you probably will want to wash it. Otherwise you don't really have to, and it's better not to if you haven't washed the fabric you used to make the top yet. If they are washed for the first time together (as a finished quilt), any shrinkage will happen more evenly. Absolutely do not rip it apart to wash it!

I usually don't wash unless it's a red and white quilt or a hand dyed fabric or something. I quilt, zigzag the edges shut and then wash the entire quilt. Once it has been dried and washed, I can see any unusual behaviour and trim it to square before adding the binding. That said, I hate doing binding so I have a few quilts that still only have zigzagging on their edges after years.

Definitely use a high-loft poly batting. Get one that's a little thicker or you can double up. It does make a fluffy quilt that will STAY fluffy.
And yeah quilting it in pieces would work. You don't have to quilt within the squares at all because you would applique the designs beforehand, and then construct the squares.

That is so great! Do you have a special machine for the machine embroidery?

No just my sewing machine with the feed dogs dropped and a jumping foot. I also have a quilting table for the machine and one of those slider sheets which helps reduce friction. I find that special embroidery machines aren't really necessary for the kind of work I do, you just have to know some tricks.

Thanks again everyone.

If you're doing straight lines you can just make a piping.  It will look neater and be the easiest of all possibilities. The other possibility is to make pressed bars which were popular a number of years ago for celtic quilts. In that case you just sew a piece of fabric lengthwise and press it with the seam at the back and applique in place. Make sure you cover the raw edges at the ends of the tubes in that case. They also used to sell rolls of cotton ribbon with fusible web on the back for these quilts, but these were quite expensive.

Cotton isn't warmer than poly but it is breathable. It's also more expensive. Typically I make baby quilts with poly because it's cheaper, and I make them to be used and therefore washed frequently. Poly stands up to wear and tear well. I might use cotton for a baby quilt if I had to, but wouldn't use wool.

Thanks for the comments.

  I hate binding and I don't hand bind. I have two techniques I use for binding, which are the least of all evils to me.

Anyway a quilt is usually defined by the fact that it is layered fabric held together with stitches, so an outer binding isn't required to make it a quilt.  I don't like the look of faced quilts myself, but they are definitely an option that has been around for a while. Works that are faced are very popular in the art quilt world, and a variety of other finishes are seen there.

I really like the texture in this piece.

I really like the print combo, and spiderweb is a great pattern. Nice work!

I have lots of quilts that have been waiting for binding for years. So I know how good it feels to finally get one of those WISPs done.