Is it illegal not to have a name?

No, but it's very inconvenient.

And if tu tell people tu don't have a name then tu might still get arrested.

do tu want a number instead?

No
Its a good deterrent against the deathnote after all

I have no idea... I have never really thought about it before.

Nope, because it´s like if tu didn´t existed.

Yes

Kind of awkward but I don't think it's illegal.

I've never thought about that...but it probably is. If tu think about it, don't tu always have a name because how will people address you? Unless tu don't live near people and aren't aware of yourself.