...fermented in the low 50s.
I'm not going to say that you can't ferment a Kölsch yeast around 50F, or that it won't work,
but I do not recommend it. In my opinion, you might as well use a German lager yeast if you're going with that temperature. Part of what I love about a Kölsch is it's subtle yet pleasant yeast character. I like the results most when fermented around 60-62F.
Recipe looks about right, accounting for lower efficiency, but are you planning on using both 2565 and 029? To be clear, in my original recipe, I list both because I did a split batch and fermented half with WY and half with WLP to give comments on both. I did not mean to suggest blending the two strains.
Youre recipe says 60 minutes, but then also says first addition hops go in at 60 minutes, so I assume that's a typo if it's a 90-minute boil. Should be at the 30 minute mark.
I think you're confused. Hop additions are noted by the amount of time that they are boiled, not how long into the boil they are added. In a 90 minute boil the "60 min hops" go in 30 minutes after the boil starts, but are called a "60 minute addition." My recipe is indeed a 90 minute boil, with the first hop addition at the 60 minute mark, meaning that after boiling w/out hops for 30 minutes, add your 60 minute hop addition.
My efficiency can kinda be all over the place, so I just went with the default 75%. I'm strictly BIAB, and I tend to get a little higher, but unfortunately I wasn't great with my note taking early on in my homebrewing adventures.
That's fine! Take note of your pre and post boil volumes, grain weight, potential points per gallon (PPG), and note the gravity you get over several iterations. After a while, you'll begin to notice a rough efficiency related to grain weight. I.e. for higher gravity beers, I tend to get 90-92%, and for mid-lower gravity beers I tend to get 95-97%. Your mileage may vary.
Also, I've always done very basic mashing. I've never attempted any kind of rests or temperature changes. I use Deathbrewer's method of mash for about an hour in the low 150s, drain the bag, and then start the boil. I'm sure this probably affects the final product, but I'm also not sure how you would get really technical with this simplistic method. I'm all ears, though.
A single infusion mash will certainly work, no doubt about that. I like the flavor and mouthfeel profile I get with a step mash, but some people can't even tell the difference. Personally, I like the malty sweetness accompanied by a nice dry finish, that I can only maximize with using a step mash. Again, don't fret about it as many won't know the difference. I know a BIAB brewer who has gotten the step mashing down pretty well. Perhaps @Gavin_C could weigh in with his method?
Cheers,
TB