Anything will help as far as magnification. I started with a regular handheld 5" magnifying glass that you can get at any drugstore. Then I got the Lighted 100x magnifier from Radio Shack (about $10) I have since gotten a bench mounted spring arm magnifier that has 3 windows 5x,8x,10x. Anything that will enable you to see the blade edge will help.
As for the sharpie, I put three(3) lines on each side of the knife bevel perpendicular to the edge apex to where the bevel meets the flat blade. Tip/Center/Back, these marks are only 1/16 of an inch depending on how large your bevel is and I re-apply after each is removed by each step in the process. That way I know when I have removed just enough material each time AND that I have gotten to the apex evenly the entire length of the blade.
As you become more proficient you will rely on the sound of the stones against the blade and you will hear where you need to spend more time, you will also see the scratches under magnification and use those as a gauge of progress.
I still use the sharpie during a reprofile where I know I am creating a new relationship of the blade to WEPS (angle/bevel size/bevel being even tip to back)
Hope I was able to paint an understandable picture, if not, please keep asking until it becomes clear. Having fun and experiencing success is what it is all about :thumbup: