I think only #1 really counts as a gotchya. #3 is literally just "spend at least 2 seconds knowing what a slice is" (which you should do! there's only like 4 data structures in Go built in, so get to know 'em all). #2 is similar.
My favorite gotchya is that assigning a nil pointer to an interface will not give you a nil interface.
Once you know what's going on, it totally makes sense, but usually you don't start out with that deep an understanding of how interfaces work, and it violates natural-looking assumptions about algebraic equality, which makes for very easy counter-intuitive behavior.
Example:
package main
import "fmt"
func main() {
var x *ErrorX = nil
var err error = x
if err == nil {
fmt.Println("nope, this won't happen ")
} else {
fmt.Println("here's my non-nil error:", x)
}
}
type ErrorX struct{}
func (x *ErrorX) Error() string {
return "hi i'm ErrorX"
}