Yes, all these forms are correct. You could also drop the "y" in "yn": 'n enw (i). In words susceptible to nasal mutation, you can leave out the possessive adjective altogether: mrawd (i). Another option for words beginning with a vowel is: f'enw (i), though this seems to be less common (it might sound a bit more formal or old-fashioned, I'm not sure). The buttressing pronouns is optional, though it's very common in speech (it can be used for emphasis, though it's presence doesn't necessarily imply emphasis).