Hi Michelle – that’s a great question!
You’re quite right that we don’t go into too much detail on that front, but that’s because this side of things is handled by WooCommerce: our own ticketing plugin doesn’t interfere with payment/checkout processes and is designed to be compatible with all of them (in a sense, it “doesn’t care” which payment gateway you use – so long as it’s compatible with WooCommerce).
Generally speaking you only need one such add-on, but if you have any doubts it is probably best to speak to the experts themselves – either WooThemes or Mijireh themselves, as those two companies are the vendors of the payment gateway add-ons you suggested (and of course WooThemes provide support for WooCommerce itself and can assist with any general questions you have on that front).
I hope that helps but let me know if you have any further questions 🙂