If you're thinking of adding spices, here's my humble offering of a couple of ideas for you.
1) Toast the dry spices. Preferably whole, and in a non-metal pan (glass works, stoneware is even better - go to lowes and buy yourself one of the $5 UNGLAZED ceramic tiles or kiln bricks. put your spices in the oven at around 350, leave them there until they slightly darken or the kitchen smells strongly of the spice.
The heat extrudes the oils and combines them on the surface of the seed pods - ultimately, you get stronger spices. Works on coriander, caraway, aniseed, peppercorns, fennel, allspice, nutmeg, etc. etc - pod spices.
Regarding the ginger, I'd be sure to peel it first. Roots - and barks - of any kind are full of tannins. Tannins are bitter and can impart an 'off' taste. ((this is why quality smoked goods are typically smoked with split, barkless hardwood))
After I peeled the ginger, I've always run mine through a microplane (or a fine shredder). And I left it in for the duration. End product was good. By shredding it, it opens up more surface exposure to the wine to allow the volatiles to mix and blend.
As far as pasteurization goes... the toasting sterilizes the spices in the case of the corianders (and will make the fragrance stronger), and regarding the ginger - a thorough peeling (as it is a root, and not exposed to wild yeasts for most of its life) and a prompt wash before being put to work should keep your project safe. I wouldn't sweat this too much.
Other might have a different opinion on this. It's up to you and your personal acceptable paranoia level. Pasteurization begins at 161F @ the core for 15-20 seconds. That's the floor of 'pasteurized'. Some bugs/yeasts can get through that heat - so it's not uncommon to user higher heat. The scope for a pasteurization discussion is probably beyond this thread.
Regarding amount, I have success with 1 - 2 tablespoons of whole coriander per gallon. (Ground up it measures obviously less - it's just easier for me to work with whole berries). Ginger, I'd say a good chunk, about 3 inches long ('thumb-sized') per gallon. That's where I start, and I'm happy. Obviously, adjust to your tastes.
What do you intend to use with the rest of the blend? Grape variety? Yeast? I'm just curious.
Good luck!
- abe