First grow many questions lol please help!need to learn more from experience not just the web,Thanks

Ok so...my first grow,autoflowers,I think I have a few issues and would like some advise on what I should do to change my room.First I am making sure ph correct with just cal mag and seeing what that does.I dont have a dimmer yet and was wonder if my light is to close or maybe I should hook up my other one now.Also one of my plants just got this brown mark over night.the 4 biggest are the same and started the same time 2 weeks ago,one is bigger but I still think they are small for their age.The others was started like 4 days after and are pretty small.I am ordering timers so my outtake turns on enough.should I get a co2 or just use a fan to suck in air from inside(outside will be to cold)and call it good?I know I need to get that taking care of,just looking for advise and see what people think.I dont understand I just started 2 and one is taking of like crazy and the other never came up.I germinated both the same.same thing with that picture of the one that's dead pretty much,should I just pull it?The root was messed up a little,the coco is damaging the roots is what i think has been happening also.Any advice helps!Thank you!

Forgot these 2 should I pull this little one?something was wrong with th root I pulled the coco out a little,found the root and seen in the middle was damaged kinda dead,gave it a chance but still not much.Probably pull.I am thinking be easier with them,the other one I think I didn't have it low enough and the light effected it and it didn't grow.The other took off so It had to be something like that.I will get it,just hope I can come out with something decent and not waste all this time.

First buy a bag of soil. Dirt. Terra firma.

Next forget autos. And read some of books @BigHornBuds posted.

Forget CO2.

In short KISS.

Hopefully you rinsed and buffered your coco before planting in it. You'll need to manage your pH for a coco grow. And you'll need to feed more than just CalMag. Straight coco is relatively inert; you need to add the nutrients when you water / feed. Despite what some will say, you need to start feeding these pretty much right away, just go easy on the feed %. Otherwise, be patient. They're little plants in giant pots. They are doing more growing underneath the surface than what they are above the surface.

I did,I have the sensi grow A and B grow and bloom.coco is good don't need soil/dirt.Closest thing to hydro with great results.Yes you should rinse but my bags come ready to go,and might rinse anyway from now on.Like I said trying to get info from experience with autos and so on.One got a little nute burn.Autos are a lot more fussy so I am trying to find some tips and trick is all.Also it's cold so my air flow is limited.I ordered a bag of the co2 and many people say they have done test and it yields more with bigger plants,especially if air flow is limited.I appreciate the free book link and any good advice.Why else would anyone be on these forums,but to learn,help and discuss?Any positive feedback,advice,tips and so on is appreciated!I have researched none stop like I said!some thing's only experience/experienced can teach,and second opinions are good.I will figure it out and will succeed!Thank you!