I won't recommend you to only buy bitcoin with your salary and save it. try to earn bitcoins from various sources and then save it all. There are many ways to earn bitcoin like Signature campaign, Gambling and trading. Try any of these methods which suits you and accordingly save your earned bitcoins.
IF you want to use your salary income to buy bitcoin, then I won't suggest you to go beyond 8-10% only. Like any other investment, start a SIP which is known as Systematic Investment Plan for bitcoin. Invest a certain amount at a certain interval. It will average out your bitcoin purchase price and give you a good amount of profit in long term.