Do I appeal it all or do I have to state what parts I want to appeal?
You can include all or just some of the issues VA has decided . You will need to list the issue you disagree with and the VA decision date for each
I believe I missed the deadline in submitting my appeal due to VA's mistake. What evidence do I need to back up my claim?
To prove a CUE error, you must show the correct facts and be able to prove that the VA incorrectly applied the law at that time.