Yá (يا) is called a vocative article and can be found in some languages (.e.g Irish). It is somehow equivalent to the Old or Classical English "O". It comes before names to address someone (or something) and to bring attention.
Yá is the most common vocative article, but there are others that are widely used in poetry, specially classical ones.
It would be so, but typically here at the end of the sentence, the last vowel is dropped, so it becomes (fareed) only.
In fact, even in the beginning of the sentence, people (or in literature) it is common to put a pause (comma) after the vocative and then continue the sentence, which implements in this case that the last vowel to be dropped as well. Like if I want to write the above sentence again putting the vocative in the beginning, that would be like:
- يا فريد، شكرًا (yá faríd, šukran).
Anyway, the normal vowel marker in such case is as you said (-u), but I seldom hear people spell it out even in literature and classical Arabic texts (unless maybe there is a continuation of speech after the vocative without a pause or anything like that).