Personally I would keep the fire serpent or change for one with better float. Also there are some mw out there that look like fn. There aren't that many on the market and even tough CSGO seems to have hit its peak (we will see next major), there are new players all the time who want a legendary AK. How far it can rise in price - i don't know. But 50% percent is realistic imo. It's just one of a kind.
At the same time you have the problem with the vanguard case. It's just not that popular. So if youre lucky you make 100% winnings there over a year. Breakout will be the same just later. And Phoenix will take forever to rise, maybe you're back already when they get scarce and rise in price.
With Chroma Cases it get's interesting. They are the only ones who offer new knife patterns and also have the Chatterbox and M4 Dragon King. Both are liked. the first more than the last. So this might be a very good investment altough they are not bought a lot atm. - here I would wait and see. If they get discontinued soon it may be worth it.
Stickers. Definitely buy capsules of next major when they get cheap. 100% pretty much guaranteed. More, depends on look of the stickers.
Last - skins. They are not bad per sé, but you just can't make as much profit with them as with cases/capsules, that's why people tend to point you in the other direction. ocean foam, overgrowth, atomic alloy, ak redline (when phoenix stops), deagle hypnotic, death by kitty would be some solid investments tough.
there are other skins you can make more money with faster too and there are weapons i don't have on my radar that will rise a lot. I definitely can not talk for everyone's taste and salenumbers are not everything, altough they can give good info.
My suggestion: keep or trade fire serpent, sell knife and rest. buy atomic alloy fn with good float. make buy order at 0.05c for 2000 cases, with the rest you wait for sticker capules to get cheap and invest the rest of your money. when you come back you have enough money to invest heavily in phoenix cases.
criticism welcomed