What is the best way to store the bread to keep it fresh for longer?
Sourdough bread will stay fresh for the longest in a cotton bag. This will give it enough protection from completely drying out, and also give it enough breathability to prevent it from becoming too moist and gluey.
Is it better to slice sourdough bread all at once, or as you need it?
It is definitely better to slice sourdough bread as you go rather than all at once. This will prevent premature staling. The other option is to slice the whole loaf and then freeze the slices Source