When I'm washing with towels, which I usually only do with a not so dirty car and a rinseless wash like ONR I'll soak 4 to 6 depending on size of car and use a one bucket wash method. Otherwise I use a mf mitt and a two bucket method. The mitt doesn't grab hold of stuff near as aggressive as a towel so I don't mind doing a top down wash with only one mitt, and typically I'm prepping the car for a Polish anyway so I'm not concerned about my gentle technique imparting a minor flaw when I'm getting ready to correct the whole surface.
By workhorse I assume you mean El cheapo towels? Or well worn ones? Those I only use on engine, door jambs or wheels.
Removing wax a medium grade towel grabs nice, like something in the 300 range or under. And for last step or a detail spray or spray wax to freshen up a already nice detailed surface go with a higher weight nice high end towel like a eagle edgeless.
How many depends on the size of car, if your only maintaining one or doing several. Rough estimate when you fold the towels you've got maybe 8 clean squares depending on the product, if it's damp and soaks through, 4. One square for each step on a door size panel? You'll get a better idea when you do a few. Best rule of thumb is figure out what it takes to do your car the right way one time, then double or triple your towel inventory for that process.
For one, you'll always have a clean set ready to go, even if one set is in the laundry, two, they last a while, but not forever, a good towel gets downgrade to a wheel or engine towel eventually and then tossed away, by the time you've gone through several by use or accident, you'll know exactly what works best for you and reorder accordingly.
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