Welp, not clear on what to do or what to invest in, but (to me) the Key point professions will be alchemy, inscription and blacksmithing, Alchemy raiders will need flasks and pots, so steady income. Inscription for cosmetic glyphs and trinkets the first two tiers of expansion. Then there is blacksmithing that can make ilvl 300 weapons (and armor) that are lvl 110, pretty much like WoD weapons, so they may sell very well through all expansion.
Blacksmith, Tailoring, Leatherworking all can create their own BoP gear like before with Blacksmithing able to potentially create indestructible versions and can repair in the field instantly (not that big), while Tailoring gets specific cloak enchants with some unique effects like not being able to to be dazed which is going to be very useful for Tailoring/Herbalists.
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.
"Essentially the Scrap-o-Matic 1000 works like the Obliterum Forge in Legion however one major difference from Legion is that you can use it to break down any gear obtained that is from the Battle for Azeroth expansion, including dungeon/raid drops, quest rewards, world drops and crafted gear. Apart from a chance at getting Expulsom you will also get ore, gems, leather, occasional enchanting mats (from scrapping cloth gear) and other crafting mats. The best way to obtain Expulsom seems to be from breaking down rare/epic gear you obtain from dungeons and raids, killing rare elites and doing world quests, it also drops rarely from BFA uncommon quality items."
For what it's worth, I like the leveling changes, but I also think that the profession changes are beneficial. Once they removed the utility of most professions; it became more of a hobby. Crafting should be fun. When it gave perks, it was fun, but Blizz, correctly, decided that it was creating forced gameplay (min/maxers always picked certain profs). So they changed it. Well when a prof doesn't give you any gameplay perks AND it's tedious...it's not fun. Especially if you're starting from scratch and outleveling your profs because you're blowing through levels so quickly.
It is really, really a stark change of pace from WoD and Legion where just questing and killing things would result in at least a small but decent profit from a day's activities, typically of at least 1k and often 2k. But now to get that sort of return, I have to really focus on gold WQ's, not spend any money on anything that I don't absolutely have to, and do 45 minutes of Legion content.
In a few months only mats will be worth anything. At this point we have people with tens of millions of gold and people with just a few thousands. A flask takes tons of mats to make, and they will sell for well over 10k gold each, so the casual players won't afford them. When people realize that the rich guys will always take buying from the AH over farming their own mats, the prices will go even higher, then casuals will notice how expensive flasks are, and they will pick up alchemy and make more flasks, driving the prices down again.