How about objects that are male in Greek? Wouldn't it then be correct as well to say "which is faster?", for example talking about computers "οι υπολογιστές"
Yes, you can use this phrase even for objects and animals which are considered males in Greek like ο υπολογιστής, ο γάτος (the male cat), ο λόγος (the speech) e.t.c.
I don't think this makes much sense in English. When the Superlative is used, there has to be an article, both in English and in Greek. "Who is fastest?", without the, isn't grammatically correct. :/
Because it's a single syllable word. Check the pronunciation of the word on its own by clicking on it. The only accented/stressed single syllable words are πώς=how and πού=where (unlike πως=that and που=who/which). As for τι/τί, some people think the jury is still out... but it is not stressed in contemporary Modern Greek.
In another exercise we discussed how you can also (and maybe should) in particular circumstances stress μού, τού, and σού. For example to distinguish between "ο θείς μου έδωσε ένα μηλο" and "ο θείος μού έδωσε ένα μήλο".