Well... There are some neuter nouns in english that are masculine in greek,for example "ο μηχανισμός", the mechanism. So, while in english that would be "Υes, but it is new" (refering to the mechanism), in greek it would be "Ναι, αλλά είναι καινούργιος." As you see, it depends purely on what's implied. For now, you don't have get into this mess. xD It = neuter, so you'd use πρόσφατο. xP
I'm pretty sure it's not grammatically correct. Some people might speak or write like that, but it doesn't mean it's correct to do so. Unlike Greek, where there is a specific form of the verb for each pronoun, English doesn't, so you'd have to use the pronoun. It can't be omitted.