I've been through a couple of different setups and sizes over the years from 1gal to 10gal. I don't even drink beer every day so a 5gal batch often lasts way beyond the timeframe I want to drink it.

I've settled on 2-5gal batch sizes now, and mostly do 2gal batches with the occasional 5gal if it's for aging or specifically sharing. There's not much to it in regards to scaling down, just use a recipe calculator to scale because it's not linear. Dead space, volume of wort in hoses etc. of course have a much larger impact on smaller batches, so keep that in mind.

The hardest part for me is getting a setup that does both 2gal and 5gal well, I haven't found a "one size fits all" setup yet. But what I have now can do medium-gravity 2gal batches to 5gal medium/high-gravity batches. If I want a 2gal batch <6% ABV it's doable but not as easy or efficiency is complete shit.