A recorded audio clip will be fine until you stretch or cut it. Right-click the "Snap" button in the control bar and it opens snap to grid preferences.
One of those preferences is "snap to nearest audio zero crossings". It's been there for many versions od SOnar.
If you then set the snap to grid to a low number of samples you can then cut clips anywhere and it will be on a zero crossing.
As for fades, Sonar can do clip fades automatically (or as near as matters). Select the clips you want to fade, click on the "clips" menu in track view and one of the functions is "fade clips". Where you also get to choose the type and length of the fade. Far better than a "one size for everything" approach.