How many levels you need is dependant on what you're trying to make. If you want to make morts you need either 8 levels or 4 levels and a shop. But if you get more that 4 levels and you still have your shop, you can make even more potions.
I like Alliance money. All jangly and nice. Marcena has little need of it, though. She needs but a couple gold for production, then some silver to gamble with. Her food is often paid for.
It's amazing what people are willing to pay when they really need it. Best sell the fun stuff. Death, hallucinate, intoxicate and amnesia are the money makers where I come from. I've sold amnesias for two gold a piece. Even when I would've only asked for six silver.