Learn German: Das Ticket ist auch sehr wichtig! - The ticket is also very important!

Good catch! There is no accusative case here because the verb is ist (is). The verb sein (to be) acts like an equals sign connecting the subject (das Ticket) to a description, rather than doing an action to a receiving object. Because of this, everything stays in the basic nominative case.

Is the word "Ticket" really German? And why is it "das" Ticket?

Yes, German borrows many words from English! While not every borrowed English word is neuter, a very large number of them get the das article. It is always safest to memorize the article along with the word, so learn it as das Ticket.

Why doesn't the adjective wichtig get an ending here? Shouldn't it be "wichtiges" because of "das Ticket"?

Adjectives only get special endings when they come directly before a noun (like in the phrase "ein wichtiges Ticket"). When the adjective comes after the verb to describe the subject, it always stays in its basic, unchanged dictionary form (wichtig).

How do you know what order to put auch and sehr in?

They simply stack up in a logical order right before the word they describe! auch (also) comes first, followed by sehr (very), and together they modify the adjective wichtig (important). It translates word-for-word to "also very important".