Resting the file on a scrap block works, sure, but it only fixes half the problem. The block keeps the file at height, but it does NOTHING for the rocking that Forman called out, because your wrist can still tip the file off the block if you are pushing uneven. What fixed it for me was choking way up on the file and letting the handle end hang out past my pinky instead of gripping it like a hammer. Short strokes, like 3 inches, and let the teeth do the work instead of your arm. You will feel the file go flat the second both ends stop chattering. Also, a light pass with a fine file first to knock the burr crown off means the big file never digs in and starts the rocking in the first place. Try the short strokes and you will cut that 4 minutes even more.

47 plugins and no backup" sounds like every site I've ever touched, that part isn't really a horror story, it's just Tuesday. The 50% upfront thing seems like overkill for a simple plugin job, most clients would balk at that.