You may get away with: Cymro ac yn falch (Welshman and proud) or Cymraes ac yn falch (Welshwoman and proud)
Draig Cymraeg
"You are Welsh" = Rwyt ti'n Gymreig
No in Welsh is dim.
Sut wyt ti? (informal / singular - like the "tu" form in French) Sut 'dych chi? (formal / plural - like the "vous" form in French) Or 'Sut y dych chi?'