Student or Learner
"To the first of many crazy things we do together."
"To the first of the many crazy things we do together."
Welcome to the forum, taab. .
It is difficult to answer without more context. If you have planned to do a crazy thing, and believe/hope this will be the first of many crazy exploits, you might drink 'to the first of (the) many crazy things we are going to do together'. 'The' is more likely if you have planned the other crazy things, less likely if you haven't.