Dashlet which pulls all with date less than X from accounts?

We are wanting a dashlet which does the following:

For each in Accounts,
If Date of Next Tax is < 3 months,
Show in Dashlet with clickable and sortable control. Have the name of accounts link back to the account.
Else, ignore.

Would this need a new module or is it a case of making a new custom dashlet? or both?