As a person who cooks quite a bit, I understand that usually things turn out best if you make more - for instance, when I make lasagna, I never make fewer than three at a time.
But I was thinking about starting smaller than 5 gallons - 2.5 to 3 or so, just to get the hang of it. Is it safe to bottle the stuff when it’s still fermenting a bit?
There is a beer making supply place not super close, but I can get there.
That's how they get bubbles in bottles.
Yes, in general you add some malt to re-vigorate fermintation in the bottle.
I prefer my own bottles with a capper over using old Grolsch bottles -— never fully confident the rubber “caps” get clean.
It’s not like they are expensive.
Someone else may come along here to say that 2.5 gal. carboys are available but I can't.
No...and yes. Here's the deal. Your wort starts off being attacked by the yeasties, who break down the first and easiest carbohydrate bonds. This is "primary" fermentation, and you get lots of foam, called "kreuzen." As those carbohydrates are broken down completely the yeast shift metabolic gears to work on other bonds (the ultimate result of which is ethanol, a VERY simple carbohydrate). This is "secondary" fermentation. Lots less foam, still not safe to bottle.
When all this stops you're ready to bottle. What you do is add a very little, carefully controlled amount of malt just before the bottling. This wakes up the yeasties and carbonates the beverage in the bottle. That's the only kind of fermentation that's safe. Bottle too soon with secondary going on or overestimate the amount of bottling malt and you get a bottle full of foam or little popping sounds coming from yer basement...which is bad news because it tastes bad after you wring it out of a mop. Don't ask me how I know that... ;-)
5 gallons (about 2 cases) is the standard beer-brewing batch and recipes (as well as equipment) are pretty well standardized to that quantity.
Besides, that gives you enough beer to drink while the next batch is fermenting and conditioning...