Good for you, man. I myself currently brew 1.7-gallon batches most of the time (that’s a 1/3 size batch compared to 5 gallons). And yes, that’s all-grain – it’s so easy to brew small batches, I love it! This gives me a little more than a 12-pack per batch, but not like 2 whole cases of bad beer if it gets screwed up, so the occasional dumper is not so emotionally exhausting! Plus I have way more variety in my cellar. Right now I have 12 different homebrew batches on hand – sure, I only have 6 or 8 bottles of each usually, and only 2 or 3 bottles left of a couple batches at any given time, but that’s okay by me. When I run out, I’ll just brew more! I find the brewing to be as much fun as the drinking anyway!
All the ingredients, including yeast, scale down. If you used one packet of dry yeast, or two vials of liquid yeast, or whatever in the past, you’ll use half as much or 1/3 as much or whatever based on the different batch size. The only other adjustment you probably want to consider is based on your boiloff rate. If you usually lose 1 quart or 2 quarts of volume in the boil, this will stay the same way for smaller batches. So, maybe instead of starting with 5.5 gallons to boil down to 5, or starting with 3 gallons to end up with 2.5, you could be down to 1.5 gallons to boil down to 1 gallon. So you’ll lose a huge percentage of volume in the boil compared to before. Something to keep in mind. Boiloff rate is constant when measured by volume, but percentage-wise it is NOT a constant for different batch sizes.
Another thing to keep in mind is how much trub you’ll lose. In a small batch, like a 1-gallon batch, if you have a quart of trub in there, you’ll only get 3 quarts out of the fermenter, and that’s only 7 or maybe 8 bottles if you’re lucky. That’s not a lot of beer! Which is why I’m an advocate for brewing at least 1.25 gallons if not 1.7 gallons like I do. Then you’ll get a good 12-pack or more for certain, and it won’t feel like such a waste of time for so little beer.
There’s many advantages to brewing smaller batches, a lot of people will just never understand. Too bad for them. If you do go this path, what you really want to figure out is how many bottles you need minimum to make yourself happy… like, if it turns out great, do you want 7 bottles? 10 bottles? 14 bottles? 25 bottles? Then just scale by 1/2 or 1/3 or 1/4 or whatever you like. You’re not restricted to 1-gallon kits. Get the 5-gallon kits if you want, or design your own recipes!, and make any batch size you want. I still play around, sometime making 2.5 gallons, or 2 gallons, or anything in between. But usually 1.7 gallons. Just seems the right balance for a guy like me. Figure out your own balance, and go for it.