IMO marinades are really fun to experiment with because you can just taste them. I cook a lot of veg proteins (tempeh, tofu, soya chunks, TVP, etc) and often marinade them. I'm pretty used to elaborate balances of salt, msg, acid, and other flavors. The way I test it out is just to stick a pinky in or use a tasting spoon and taste. You want your marinade to be heavily seasoned than what you're marinading of course. Acid is an essential component of a marinade.
Acid is important for meat marinades because w/o acid, penetration is just a few mm deep.
The real magic, IMHO, comes from how Indian food is spiced. Lots of contradictory flavors that are used in ways very different than western cooking. Also lots of steps involving dry roasting some of the spices, while leaving others as is, and which spices get dry roasted changes from dish to dish.
I do a lot of Indian cooking from scratch at home, and while I can slightly improvise recipes and tweak them to my taste, I am still a long way from being able to truly understand WTF is going on with some of the more complex reactions.
I do a lot of Indian cooking also and have for decades, and my suggestion is to just play around with tastes and smells. Dry roasting especially your nose is your friend. That or corner an established South Asian chef and talk to them about their use of spices :)
Acid is also really important for veg proteins because most veg proteins on their own have very little flavor. You can impart umami through various ways but umami without at least a bit of acid does not come across balanced on the palate, so you need to balance the acid with the umami.
The thing that gets me about how Indian food uses spices is that the flavors change so much during cooking.
If I use cumin in a Mexican or even Chinese dish, cumin will likely be a dominant flavor, it will be obvious that cumin is in the dish.
Meanwhile a similar amount of cumin in an Indian dish will get completely transformed and melded into a much more complex flavor profile.
Same goes for cardamom, I use a lot of cardamom when making American desserts, and its presence is obvious.
Meanwhile, my curries have cardamom in them and it adds levels of depth and complexity, but not in the overpowering way it does when used in western cooking.
