Some stitches you like in thread or yarn may not look like you expect - and that can be a good thing or a bad thing. You block wire by stretching it with your fingers. Sometimes I use a crochet hook as a pointer to make a stitch go where I want it to, or use the handle to 'fluff' a picot. Wire Breaks Wire can also be repaired, if you're sneaky. Reinforce broken wires with additional wire, if necessary.
Twirl strands together to make the wire equivalent of a knot.
I've used 30 gauge, but it's a bit fine for me. I've done most of my work in 28 gauge brass, copper, and sterling. The heavier the gauge, the more sturdy it'll be. What really stretches is the crochet stitches. How much it stretches will depend in part upon your stitch tension, the type of wire, and the type of crochet stitches you are using.