>>214620741
>日本語で上手になる
日本語が上手になる*

become good at XXX
XXXが上手になる

>日本にいる間に外国人を避けたほうが良いですか
This is completely grammatical, but I feel like the 間に doesn't fit the sentence.
If it were me, I'd say 日本にいる間 or 日本にいる間は instead.

The rest are perfect.
Keep at it and enjoy your stay in Japan.