These rules of thumb for rounding in statistics would be fine for the coursework and your project as well. As you have mentioned, some suggest that you round to one more decimal point (dp) than your original data. However, if your original data were mixed, round one dp more than the least precise. For example, consider the set 10, 8.7, 9.2, 11.4, 6, 5.3. Some are whole numbers, some have one decimal place. The least precise numbers in this set are the whole numbers, so you would report your mean and SD to one decimal place. So for your Q8 example, it would have been fine to report mean 53.3 and SD 10.4. But overall, we are pretty flexible with rounding on your HW...
For probabilities, I have seen people rounding out to 3 or 4 decimal places. The style of some journals (and the AMA) suggest rounding to just 3 dp. For example, if p=0.0003, you could report it as such or p<0.001 in some journals.