There are some very extensive video courses available, starting with this single six-hour video on YouTube:
Just searching for "Linux masterclass" there will reveal multiple playlists of videos from which you can choose what suits you best.
As for certification... that all depends on the job market.
When there are more people than jobs, a certification raise your profile among many applicants and some positions require one.
However when the jobs available exceed the qualified candidates, the expense may not be required.
The best things certifications can demonstrate is showing what you need to know. Looking at certification exam objectives can be beneficial even if you never take the exams.
- Evan
(PS: Please change the subject of this email thread)