Only two of a buch of seeds that sprouted ended up surviving. One started flowering pretty early on, despite getting the exact amount and schedule of light as the other one (they shared a pot). The other kept growing taller then died without any signs of flowers.
The post pic is from ~2 weeks ago. At the start of this week, it looked like this: 
And the leaves just kept dying.
Today I decided to just harvest it. Here it is after cleaning: 
I don't know what strain this is, because I didnt label the seeds. But it smells very citrusy and I know there were some lemon haze and lemon skunk seeds among them.
What are the next steps? I've heard I should hang them somewhere to dry, is that correct?
As mentioned, a cheap hygrometer is 100% worth it for curing. You want to stick it in a jar and open it daily (called "burping") until the hygrometer reads 60%. There's a huge difference in flavor like +/-5% from that number, I learned the hard way.
Despite it being called "weed", cannabis seems to be extremely tricky to grow in containers. The fertilizer and light requirements are very specific, and failure to meet them usually means you kill the plant early on or just get a poor harvest. It took me three tries to get a harvest initially and it was a LOT of work and initial investment, but it was fantastic quality flower.
Some tips for next time:
Do not use miracle gro or any other standard potting mix - the fertilizer ratios are not good for cannabis and usually it will fry the seedling before it even gets a chance. I had good results with coco coir.
They need a ton of light, if your balcony isn't getting 12+ hours of direct sunlight it's going to reduce your harvest. Mine stayed in a grow tent the whole time and received 16 hours of intense light through most of the grow cycle.
Autoflowers can be grown in smaller containers, but you want 5+ gallons for feminized plants.
Fertilizer ratios and pH of the soil matters A LOT. A cheap pH meter is a great investment and could mean the difference between several ounces and nothing. Fox farms makes great fertilizer and fertilizing schedules can be found easily online.
Coco coir is notorious for holding onto salinity due to it's ideal CEC so if you don't get the low-salt stuff or you don't know if it is, give it a very thorough flush. In fact, I'd do that anyway just to be on the safe side.
I've never grown cannabis before (not a bit btw) but if your coir is too salty then I can't imagine cannabis is gonna take well to it.
(In fact, it shouldn't be all that hard to go media-free and this could eliminate some variables, but that's a topic for someone who knows what they're doing with a cannabis grow.)
Just make sure that you understand how to store a pH meter so you get accurate measurements. Unfortunately they are much more fickle and delicate compared to tools like thermometers.