Celt
You started the thread so you can take it where you want to go. No worries about hijacking.
I applaude your "understand before taking the test", but I have a different view.
Although studying for all three elements gave me new info on the subject, I learn more after getting licensed.
The rule are set up and as long as you follow them, go for it.
If you can afford a HF radio now then by all means, study and take the test.
There is a 11 yo girl Faith Hanna who just passed her Extra and is one of the hottest "gets" when she is on the air. She certainly does not fully understand every segment of the Amateur Extra material but she passed the exam and has access to all of the "Extra" bandwidth and privileges. She passed the exam and as such is entilted to those privileges.
https://www.qrz.com/db/AE4FH/?mlab=Her sister Hope 9 yo just gave a talk to Old Diminion University Engineering School on ham radio satellite comms.
You goal should be to pass the exam and then promise to continue to learn. Strive to be the best operator you can be, and DO NOT BE LIKE THE GUYS ON 14.313!!!!!