Bitcoin investments is a very promising investment which although seems to be of long term returns.most persons are not patient enough to wait till the value of Bitcoins rise significantly .
Soo in general how much should one invest in Bitcoin should it be "how much you can easily invest without stress " or "as much as you can invest at all cost"
Although I am aware it isn't a do or die affair
Well, an investment to begin with is something that you should devote some time to. If you want to invest on something that is "stress free" like you mentioned, then I guess it is better to allocate your resources in stocks by purchasing blue chip companies' stocks in the process.
Investing in cryptocurrencies is definitely risk in itself. With its volatility high, its price may change without any given notice. That is also the reason on why majority of the people invest in BTC either for short/long-term depending on its price on the market.