As far as hand wet sanding the other fender goes, that's fine, as long as you use the palm of your hand...I think we virtually have the finger sanding worked right out of you...and that's a good thing. If you do sand through to bare metal, those areas will need to be spot primed.
Guide coat...at Menard's...I am from Canada, we don't have a Menard's...we just got Diet Coke, I don't think Menard's is thinking of an expansion to Canada no matter how much we want guide coat...LOL. If they sell Lacquer Primer in an aerosol can, then Menard's has has guide coat. If they have it in Red or Red Oxide...that would be better. The reason I suggested lacquer primer in an aerosol can is because it dries quickly, doesn't clog sand paper that fast and Red will work for the Black E Coat and the the Gray Epoxy primer that you will be putting on later. Also the price, 3M makes a guide coat which works great but it's way to expensive for what your doing...Lacquer primer was probably the first guide coat made. If they don't have lacquer primer in anaerosol, an automotive store may be where you need to go.
When you sand your bumper with the Scotch Brite pad...no need to guide coat it...it's plastic and your not going to straighten any high or low spots...just rough it up with the pad and warm soapy water.
Now seriously...after I fell asleep at the computer last night I woke up and had this vision of your "Wax and Grease" remover being "Wax and Tar Remover"...is this just in head or do you in fact have Wax and Tar remover?
Also, what brand of base coat are you planning on using...we are going to need to figure out the color. I know you have a code, but, many codes have numerous formulas so it's going to be a trip down to the paint store with either the car or a fender or something with the color of the vehicle on it. They need to check the color to the variant chips that they should have at their location. After we get the paint, we are going to need reducer...maybe if you slip the guy at the paint store $5 or $10 over and above the cost of the paint, he will mix up a pint of base, throw it in a quart can and add the reducer for you...it would save you buying a gallon of reducer.
If you have more questions, ask away.