Recipe ranks basically make you more efficient at making stuff, either by letting you craft the same number of items for fewer materials or getting a higher yield from the same amount of materials. As an example, having a one-star rank recipe lets you craft items at a relatively inefficient way, but when you acquire two-star or even three-star recipes, it can almost feel like you are crafting items out of thin air because of the low amount of materials required for each craft.
Consumables (Alchemy, Jewelcrafting, Enchanting) – When I have gotten a toon to max level and managed to get all of the end game recipes/ranks, I have done well. However, I never have much luck with the lower level items. It feels to me like if someone is going to buy a gem, enchant, or flask, they want the best one or none at all. Maybe that comes down to the servers I play on, but it does make sense compared to how I play my own toons. I either am going to gear up a toon for endgame or not worry about it at all. Alchemy does have the benefit of transmutes which even the low level ones can make some decent gold. JC does have the MOP mounts and pets if you can get the recipes for them but otherwise these professions feel like max level or bust to me.
I think that's server dependant. I make a lot of Golems, but the price on my server is high enough that you could buy all the living steel and still make about 20K (almost 200kg on AH). Its just that you proc all the way up the chain. You proc 20% of your trillium, and then 20% of your living steel. SoH and Ghost Iron are such low effort farms, too. 20% of 180 Trillium Bars at 500g is 18k more profit, 20% of 150 Living Steel at 3500g is another 105kg. That's an extra 25k profit per Golem. If they stop selling stockpile them for the next expansion, they always boom with the price of herbs. And a consistent 20% proc rate is the opposite of RNG, its extra free stuff as a benefit to completing an extra quest (not to mention for new alchemists the investment of leveling Vanilla Alchemy). You're looking for some get rich quick scheme, where the real way to build wealth is patience and volume. No market is going to be viable because you want it to be. Only because you make it viable.