without a memory card you can have eight 4-second samples on the SP202 if you're recording in 'hi-fi' mode. you can play back four at a time depending on length of the sample and what, if any, on-board effects are active. i've never really used the boss RC-2 (or the bigger one) so i can't comment on that, but if you do all your sampling beforehand using the SP202 live is pretty intuitive.
with the setup you described, it sounds like you're using two mixers? you could save space by running an aux send from your mixer into your effects chain so you can dial in signals from different mixer channels into the same effects.