Welsh is phonetic - as long as you know what the letters are to be pronounced as its easy
bear in mind Y is a vowel pronounced like the e in easy
and ll and ff are really letters in their own right
ll as in llandudno. ff is pronounced like an english f. a single f is pronounced like v
So it should be possible for an English person, with a little training, to pronounce Welsh reasonably accurately.
It's a little more complicated than that, Welsh is mostly phonetic but that doesn't mean every letter is always pronounced the same way, it can depend on context - the letters surrounding (or not) a particular letter.
Your example of Y is a perfect example. It's not always the equivalent of "ee" (probably more often than not it isn't)
It can be "uh", "i" as in "bin" in English, or "ee".
For example
Ysbyty (hospital) = uh-sbuh-tee
Y (the) = uh
Dyffryn (valley) = duff-rin
Bryn (hill, or common Welsh name everyone knows how to pronounce) = brin, not breen
Then there's when a vowel combines with another, e.g. the "wy" in Dwygyfylchi. Which is completely different to the "wy" in "Conwy", where the W acts as a consonant, not a vowel.
Welsh is easy to pronounce, you don't particularly need to learn any arcane rules, but you do need experience of letter combination sounds, and put the strange "vowels are A, E, I, O, U" thing we're all taught about English out of your head. (Which doesn't even work in English!)