Hi Zohan,
You should be able to set up an SD card with multiple operating systems, here’s a guide for a few different setups including multiple on the same SD card
The NESPi case has active cooling so depending on your climate should be able to keep up with an OC’ed Pi!
In regards to performance, it’s a bit hard to say for sure without knowing for sure what software you were using and a wide range of other factors. It really just depends on how well optimised the emulators are.
I would recommend checkin out these links as well!
https://www.google.com.au/search?q=retropie+rom+setup+site%3Ayoutube.com
Cheers,
Liam.
