The brushes they use aren’t clean often and contain dirt/rocks that would scratch up your car.
Also soaps in normal and touchless car washes could be acidic, which is good to remove things off your car, but it does reduce the life of the ceramic coating.
The sun is your enemy during washes as you have to work quicker so soap / water / product doesn’t dry up on your car.
Wash during cloudy periods or in the early morning / late evening for an easier experience and better results.
You want one for clean soap, one for dirty water and you could have another dirty water bucket just for your wheels.
The reasoning is you don’t want to scratch your car using a dirty sponge/mitt. Using 1 bucket contaminates the soap and potentially keeps dirt and rocks in your sponge/mitt as you rub them on your car. Wheels obviously contain the most dirt, iron and debris so avoid using the same tools and bucket for the body of the car.
I like to work on the glass first since it’s easy to scratch glass and it’s very noticeable when damaged. With a new clean soapy sponge, there’s way less risk to damage the windows.
There’s a lot more dirt/debris near the bottom of the car so getting that in your sponge and rubbing it everywhere else is no good.
There’s a reason why dish soap is for dishes and facial soap is for your face. Those soaps could be more acidic, mildly abrasive or ineffective against cleaning your car. You may end up stripping off any waxes / coatings applied.
So don’t be cheap to try to save a few dollars, use PH neutral soap formulated for car paint.