How Do I Not End Up Broke at 25? (18 y/o here)

Here’s my situation: Just turned 18 (living in New Zealand) and I’ll be starting university next year (majoring in engineering) My current finances/investments (if you can even call them investments) are:

• $8000USD in cash
• $4700USD invested in sealed Pokémon products
• $3500USD purchased car
• only make $150USD a week working, and I also run a small watch business which makes sporadically 50USD-200USD a week

Was wanting some advice on what I should do to make sure I’m financially comfortable in the future, should I start investing weekly in a index fund? Should I sell the Pokémon stuff? Thanks for the advice