The maximum storage capacity seems to be 2953 bytes ([1]).
Although that's with error correction level L, so you can only read it as long as you have 93% of all codewords.
Author here. The amount of data per QR depends on the QR size specified. If I remember correctly, its about 10 bytes per code in the default config (QR code size of 30). Transfer boilerplate is a few codes in the start to setup the conversation and a FIN like message at the end.
