No one can tell you how much of your montly in come you should invest, that's entirely up to you. Standard answer is to "invest what you can afford to lose" but realistically, majority of people invest more than that.

What can I suggest you to reduce amount of stress is to to stop looking at the price on the regular basis, especially if you are into it for a long term hodl. Few years ago I deleted all the price tracking apps and i have to say that it helped me immensely.