1 and 2. I check back my dissertation, I actually used 5 volume of -20 C acetone. There was no mention of incubation time. I did the precipitation in batches using a 4-liter plastic beaker. I just stirred well and recovered the precipitate with Whatman #1 filter paper in a Buchner funnel. I started one beak of acetone precipitation while I filtered the previous one. So the stirring time is 30 min at the most. When all precipitate are collected, I rinsed it with cold acetone and allowed it to dry in vacuuo (with continuous suction).
3. The choice of buffer used to dissolve the precipitate depends on the solubility of your protein. I used 0.2 M ammounium acetate, pH 6.8 and ran gel filtration with the same buffer. Not all the precipitate will be dissolved in the buffer. You need to adjust the pH of your suspension and centrifuge to remove the insoluble material prior to running on columns. Otherwise proteins start to precipitate when the pH of the protein solution changes as it moves down the column. Keep the insoluble material frozen until you are sure you got the protein you want. You can do another extraction with buffer of a different pH, if necessary.
4. My protein is very soluble at pH 6.8. However, since it was extracted using HCl-acetone, I need to add NaOH to adjust the pH to 6.8. As I have said, not all precipitate is soluble, so I just centrifuge to remove the insoluble material (it is a purification step!).
Not affiliated with any company. Mention of a specifc product does not imply my endorsement of the product. No conflict of interest or guarantee to work on the advice given. Do as I say, not as I do. Not liable to the loss of your valuable samples.