I own 2 401A Singer Machines and love sewing on them. I use mine every day both were bought in the 60's. I also have a new Bernina Computerized but do the majority of my sewing on the Singer.
To answer a couple of your questions for regular sewing you need the middle knobs set to A and K.. with the red lever in the center. This should result in a great straight stitch. When I free motion quilt I have the throat plate in the "UP" position, this puts the plate just above the feed dogs and works great.
The machine came with 5 cams but you could buy additional cams to do more stitches. The cams for this machine are black. The footpedal for this machine has a small button on the left side for operation, the hinged knee pedal will strike this when installed in the correct position. But it also works well on the floor too. I use mine both ways depending on the cabinet. I bought a new set of cords off ebay, do not remember the seller's name but it stated for 401A and works great.
When you wind the bobbin, you need to turn or loosen the silver wheel inside the main pully wheel so the needle does not operate when winding. Then retighten when finished.
This machine uses a class 66 Singer bobbin. I have also purchased a 1/4" foot and a free motion foot that both work well from ebay. The ad stated they were for 401A and have used them daily with no problem.
If I can answer any more questions or help in any way... let me know. I don't always read all the post so feel free to message me.. I will get it for sure that way.
Jackie