Below is a screenshot from Ally.com. It shows me going through the process of transferring money into a savings account that has buckets/envelopes. In this example, I am attempting to transfer in $1,000 USD and can divide it among the 6 buckets however I see fit. What I think Ally does well here is that they display (to use your terms) a) the maximum and b) the sum of the range inputs; doing this gives the user greater visibility “behind the scenes.” Furthermore, Ally attempts to prevent errors by showing me a message at the bottom of the allocations column, telling me how much under/over I am to my maximum—I might have expected the button to be disabled until the sum == the total I am transferring, and for the text to highlight red if I am over.
I’m sure this puts a bit more responsibility on the user to make sure everything adds up, but I think it reduces overall complexity on both you and your user, eg do you set a max value of the slider or disable goals if the maximum has been met, and from the user perspective the slider isn’t the best UI element for granularity. Plus, I imagine the complexity increases with each additional goal a user has.
I hope something in here helps! Let me know if you have any other questions, and definitely let us know how this turns out.