Really really rarely. Maybe if your grandma is talking about her boyfriend back in the day.
Nope. It's just "new" and it only makes sense in quite limited contexts. The new boy in the school, for example.
The introduction told us that SOME masc. adjective ends in -i and SOME neut. adjectives ends in -ie. But is was not clear if the change is fixed (i -> ie , y -> e), or if we can encounter irregularities