I'm not much in the business of diagnosing others, so instead of properly answering your question I shall simply share all the information I've gleaned from my 15 some-odd years of dealing with Tourette's myself.
1) Firstly, in order to be considered Tourette's and not simply a tic disorder, one must exhibit vocal, which can be anything from excessive throat clearing to blurting out random phrases, and motor tics for a duration of over one year. If I'm not mistaken, tics which last but a year are considered Transient Tic Disorder.
2) Tics often wax and wane-hell, there are even instances in which I've not ticked for so long I think I've been miraculously cured. Likewise, there have been long, unbearable stretches of time within which my tics have been so difficult to control they've caused certain things to be rather difficult. When they act up like that, you simply never want to leave your room because you know what a bloody weirdo you look like.
3) The severity of tics seem to be affected by environmental stressors, such as allergies and heat, as well as internal stressors like anxiety or excitement. I can definitely verify the validity of this claim, however, tics seem to decrease and increase in severity quite randomly as well.
4) Most with the disorder have had tics since they were in elementary school.
5) I've read those with Tourette's are more likely to exhibit ADHD, OCD, and other anxiety disorders. I've read those on the Autism spectrum tend to exhibit Tourette's as well.
6) The way you describe holding in the urge to shake your head is an absolutely perfect description of how it feels to hold tics in, though I believe that example was more than likely prescription-induced.
7) A lot of people confuse tics and stims, but because I do not have much first-hand knowledge on stims, I do not believe I would be of much help explaining the difference. I can only say with certainty that stims are voluntary and usually to comfort oneself in a stressful environment, whereas tics are not voluntary. A person with Tourette's can "control" their tics in much the same way a person with OCD can keep themselves from engaging in ritualistic behavior. Perhaps that is the same with stims though...
Hopefully this was somewhat helpful.