Are you a

Buick?

I won't say yes 6 months from now

I'll say "Aye" (I) -long

Cast your net, as soon as possible

Into the sea (C)

To Kevin Spacey: Who won the sequel?

I don't actually know what this refers to, but judging from Hint 2 I would assume the answer is "You" (U)

Play me once but skip the major

We're playing a musical scale that includes the note (B)

I'm not a Tesla,

I'm a BUIC

Aside:

Is the "sequel" a competitive event won by the UK?

Are you a

Buick?

I won't say yes 6 months from now

I'll say "Aye" (I) -long

Cast your net, as soon as possible

Cast your net into the sea, sharp! (C-sharp)

To Kevin Spacey: Who won the sequel?

I don't actually know what this refers to, but judging from Hint 2 I would assume the answer is "You" (U)

Play me once but skip the major

We're playing a musical scale that includes the note (B)

I'm not a Tesla,

I'm a BUIC

Aside:

Is the "sequel" a competitive event won by the UK?