New Cavalier owner!

I’m about to adopt my very first cavalier and need advice on what to know! I currently have no supplies & feeling a little overwhelmed starting from a blank slate (although I’ve had family dogs before).

Ladybug is a tiny 5 year old rescued from a breeder and is just the sweetest. Main questions:

1. Collar or harness?
2. What type of dog food?
3. Treat favorites or to avoid?
4. Any special tools I should get for care?
5. Anything else important to know for this breed!

Thank you in advance!!