[Sashimister]

RickOShay is correct on 森 and 林.

Your second question is somewhat tricky. This is a kanji question, not a word one. Yet you make it sound like a word question and people tried to answer as such. The word "synonym" is NOT used when comparing kanji. It's reserved for words.

We use 晩 as a word, but seldom use 夕 as such. The latter is almost always used in compounds such as 夕方 and 夕食.

Even as kanji, there is a difference in the meaning between 晩 and 夕. 夕 is the early evening and 晩 is mid and late evening.