1. Grip
I use a mixed grip as it’s the most universally stable grip. If you have big hands or more specifically, long fingers, you can try an overhand grip but most people just can't hold heavy weights that way. I never use straps but it’s not uncommon for good lifters to warm up with them to save their grip for heavy pulls. Others will use straps when doing reps so the grip doesn't become the limiting factor. Research shows that using a mixed grip instead of an overhand grip can help you get an extra rep or two when training.
2. Foot Spacing
Yes, this matters. Some coaches and pros insist on particular foot spacings as being optimal. When I asked the legendary Ed Coan for advice on deadlift, he told me he would have to see me grip the bar. What he meant is that everybody is shaped differently – arm length, torso length, leg length – so it’s hard to know what your best position is until you grab the bar and start lifting and analyze your own leverages. That answer prompted me to fly out and train with Eddie. Most people perform deads with a narrow stance. As I gained weight I had to start adjusting my stance outward a bit.
So my general answer to this type of question about foot position on deads and squats or hand position on bench is to train a variety of different widths and over time you will settle into the stance where you are strongest. There's no one-size-fits-all approach.  
3. Breathing
For powerlifting, I always take in a huge breath and hold it just before I lift. This creates intra-abdominal pressure that allows me to explode like a coiled up spring. Conventional wisdom is to exhale upon completion of the lift but I always tend to exhale immediately after breaking inertia on the deadlift or after exploding up from the bottom of a squat.
4. Coordinate
When I lift, I’m not thinking about my hips or my low back or this or that – I’m thinking about keeping everything tight and using all of my muscles together to pull the weight. I activate the core, legs, glutes and back all at once when initiating the lift. 
5. Depth
The depth of your glutes on the deadlift is based on your own body mechanics as mentioned earlier but generally speaking you want your legs at 45 degrees so your back, glutes and quads are all activated when initiating the pull. Go too deep and its all legs. Go too high and it’s all back. Some great deadlifters like Michael Koklaev squat way down before lifting but if you look where his hips are when he actually applies tension to the bar, they form 45-degree angle with his legs and back. 
6. Head
People tend to differ in their head position for the deadlift. I keep a neutral head position. It's never a good idea to exaggerate the bend of the neck. 
7. Miscellany
The deadlift is not a golf swing. It shouldn't be over complicated. Some technique is good in order to avoid injuries while learning how your body responds to the forces but over time, once you're able to control your core, its really about brute strength. That's what I love about the lift, you just have to man up if you want to pull really big weights. Most people fail mentally.