You could keep some small koi in here for a little while but it's not big enough for even a single full sized koi. You would also need a lot of filtration, multiple 55 gallon drums. It could make a nice quarantine/treatment tank for koi if you had a proper pond. Otherwise you could keep goldfish in it.

Roofing felt? Do you mean EPDM liner? You would have to line the inside of the totes if you cut one side off like that. The frame is needed for structure if you are going to cut into an IBC tote. Typically, a tote is only cut out at the top because there is no really good way to join them.

yeah... I will most likely have to dig a pond anyways. Thank you for the ideas of making it a quarantine/goldfish tank instead :)

You can use a plastic stock tank for an above ground pond for goldfish if you don't want to dig but way too small for koi.