With respect to PayPal, any payment that comes through to you won't be subject to an ACH Return or NSF fees since it is coming from within the PayPal system. (i.e. if sufficient buyer funds weren't already there, the buyer wouldn't be able to send)
In terms of monthly limits, this is mostly dependent on you being verified by PayPal. What kind of monthly processing limit are you looking for and what kind of average ticket size?
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