I have read that you can use wd-40 on a paper towel to clean your strings after playing but i want to know if this will have any effect on coated strings?
Unlikely, and I would never do that to be honest, if you get WD-40 on the neck its gonna be a permanent stain, or worse. Get a proper string cleaning kit if you want to clean your strings.
That sounds like a terrible idea. I wouldn't use WD-40 anywhere near a guitar.
whats the best string cleaning kit then?
I wouldn't pay for a string cleaning kit. Wipe them off with a clean rag after you use them, that should be plenty unless you have very acidic sweat. Coated strings pretty much stay clean by themselves, there's no need to buy more things to clean them.