Back in the CiviCRM days we had instructions for which steps to go through when an externally funded project got approved.
In FortNox we have so far limited ourselves to creating a Kostanadsställe and Projekt with the given name and assigning it an id.
There is however also the possibility of setting start and end dates, along with linking the project to the funding body.
And https://support.fortnox.se/hc/sv/articles/208331025-Kontoplan suggests that it might also be possible to set the budget for the project in FortNox.