Two part question. For a 1 gallon brew how much fruit do you use and do you bag or not?
Personal preference for both parts.
For the quantity of fruit, some people will use 1-3 lbs/gallon of must. I like the fruit flavor to really POP, so I tend to use 5-6 lbs/gallon of must. It's a little more expensive, but, the final product is better for my tastes.
As far as the bags go, I personally use bags, but, again, it's really personal preference. I find there's advantages to both.
No bag, the fruit is completely exposed & easily fermented. The downside to open fruit is your fruit cap has to be punched down twice a day to prevent mold growth. If in a one gallon carboy , a gentle swirl will usually be sufficient.
With a bag, typically, less lees, clean up is generally easier, you can put fermentation weights in the bag & the fruit stays wet on the bottom (eliminating the need to expose your must so you can punch down the cap) & my personal favorite, maybe less racking , (if your lucky enough).
Typically I ferment in food grade buckets, with bags, then transfer to glass for clearing & bulk aging.
I hope this helps you.
Happy meading