Maybe you're overcomplicating with the dish with all the pastes. Every recipe I've used uses stock, lemon grass, galangal, lime leaves, lime juice, fish sauce and lots of chilli.
You can add optional extras such as tamarind, tomato, corriander, straw mushrooms. One recipe I have uses a little chilli jam.
I've never made one as good as one I had in Thailand, blisteringly hot, with pork hocks. I think it was the stock that did it.