Freedom Munitions has a great price on brass plinking ammo. But check around deals can be had. I have been getting emails from AmmoMan who has bulk xm193 for sale although I am not sure on how good the deals are.
Any of the Russion Steel ammo Tulammo, Brown Bear or the like seem to run good in the M&P series rifles, they have a waterproof coating on them that after you shoot a bunch you it seems to coat the chamber walls. Either shoot a couple of brass rounds after you shoot the steel or use a chamber brush to clean it out. As far as a cleaning kit, the Otis for the 5.56/.223 is just hard to beat, and I always recommend getting a boresnake but there is a thread here on [Tools I Use to Clean] that will give you great information, I didnt post it but the person who did gives great advice and I always trust the input from them.

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Grover Oathkeeper