First brew

Beer brewed: Kolsch

Howdy folks

I am new to this subreddit and new to brewing. I would’ve posted sooner had it not been so hard to accumulate 5 karma points. I’ve had an interest for awhile and finally broke the seal on the world of brewing, with my first batch ever going into the fermenter a little under 2 weeks ago. To be honest, I found myself not entirely sure if things were going the way they should, so I thought I would ask you guys some clarifying questions.

How much margin of error is there for things like: Sanitation, Temperature (boil vs simmer), timing (adding hops for taste at 13 min left in the boil rather than 15). Sanitation was really something I tried to make sure I did right, and I found myself stressing over little things, like a roommate walking by the batch and fearing it would stir airborne bacteria in the air towards the batch. Is that even reasonable? Another thing I was concerned about was how long it would take to get in and out of a boil after steeping the specialty grain. I wasn’t using the most efficient heating element, so it would take awhile for temperature to go up. What kind of effect does this all have? And what about how much water you start with in the brew kettle? I saw “at least a gallon” some places and 2.5 gallons in others. What effect occurs based on the difference? I ended up doing 2.5 gallons and topped it off to 5 gallons prior to pitching the yeast (while very concerned about infecting the batch while adding water).

Lastly, as I mentioned I’m almost 2 weeks into fermenting, and I think it’s about ready to bottle. (I forgot to take the OG, but I took an SG reading after 1 week, so I’ll compare that to a FG reading at the 2 week mark before I bottle). I’ve seen some videos where the priming sugar solution is made and put individually into each bottle, and others I’ve seen the priming sugar solution put directly into the bottling bucket and mixed with the flat beer prior to bottling. Any differences between these methods?

I know there’s a lot of questions in here, so thanks in advance for y’all’s help. Cheers