Hm... #1 may be difficult, but it would be nearly impossible to know the answer without knowing the detials of the scale you are using... maybe someone else will have an idea?

As for #2, your answer may be easier than you think - the 8252 comes with 2k of EEPROM in addition to the 8k of flash - which would be plenty for storing the PINs and weights - so you might consider forgoing the external altogether and just storing it in the chip's eeprom.