I want to big invest in bitcoin. But I want to know your opinion. Is my invest will profitable at this time?
It will, but not sure when. When you are making an investment, it's not about just profit but think about how long you will hit the ROI and other stuff about your emotional thingy, because those matters rather than solely about profit.
Short term investment or long term investment will best for me?
Definitely long term, short term investment on Bitcoin is dumb and you should not do that.
I saw bitcoin market price is some cheap at this time. So I can decide to bitcoin invest?
It's up to you, just do it lol. Either invest on Bitcoin or Altcoin are fine.