I think the sentence is fine, and you have interpreted 'bucke down' rightly, though I would add there might be a sense of resentment also. For example, you would 'buckle down' to a job that you may not enjoy but you know it has to be done.
'Buckle down' doesn't exactly translate as 'concentrate on', though it could mean that. So it would be possible to 'buckle down' and concentrate, they sometimes occur together, like in your example.
The phrase was commonly used when revising for my exams .
Lastly, I think the use of 'excited' is also fine. The speaker/write is saying that if the job is something they are looking forward to, then they don't mind doing it. You can be 'excited' to do something, for example many people like repairing classic cars.
Student or Learner