1) What's the difference between 須要 and 需要? Are they interchangeable?
2) This question illustrates the differences among 嘗試，試圖， and 企圖, but omits 試試看. Can someone explain how 試試看 differs from 嘗試?
'須要' (need to) applies to 'verb' e.g. '須要付錢' (need to pay)
'需要' (need) applies to 'noun' e.g. '需要金錢' (need money)
'試試看 means 'try and see' e.g. '試試看不付账单' (try not to pay the bill and see); '加些糖試試看' (try add some sugar and see)
If you remove 看 and write '試試' then it would become reduplication of '試' (try/ test) ; 試試 = 'slightly try/ test a little '
'嘗試' means 'to try (one's hand at)' As stated in the other question.
须要 is always used as 要， so in daily communication，we Chinese don't use 须要。