From 607:
(d) INTEREST- As used in this section, the term `interest' includes service charges, renewal charges, fees, or any other charges (except bona fide insurance) with respect to an obligation or liability.
This definition pretty well engulfs all fees associated with a loan as interest. Therefore you could not charge any "fee" that would cause your interest rate to exceed 6%.
Not sure about your bankruptcy question. What kind of fee would you charge someone if they filed for bankruptcy?
If by some chance you are inquiring about legal fees, that would be a matter for the judge to approve since you would have to had gotten court approval before beginning any legal collection activity to begin with.
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The opinions expressed are mine and they are not to be taken as legal advice.