In essence, yes that's it. The result you get will of course vary with the tea you start with among other variables.
Occasional shaking probably isn't enough - I generally shake my tinctures at least once a day - not an insignificant commitment over the course of a year or more. It won't hurt if you go away for a week now and then though, tincturing isn't that critical and is a distinctly inexact science.
Dark is certainly a good idea, cool is OK, warm probably better, cold not so much.
1) Not ideal
2) No, minimal airspace is fine, with some tinctures a little air is helpful to the process anyway.
3) You could do, but then it will need very careful filtering afterwards - but try it by all means - the more finely powdered it is the faster the tincture will be ready to use. But it may also result in a slightly different scent.
4) Mainly space - a full jar of unpowdered tea is pretty full at 10% - remember it's done by weight and dry tea doesn't weigh much. If you are using other materials, dry them first or the water in the leaves / flowers / whatever ends up in the alcohol resulting in clouding problems when you use the tincture in your perfume.
What you're paying for when you buy a ready-made tincture isn't so much the raw-material but all that time, trouble and storage space that went into making it. Also if you want some today, you have to buy it, if you want some next year and you enjoy spending time playing about with tincturing then hang on to your money. . .