It will not be a good decision to invest all your money in Ethereum though it will not give you any loss . You don't need to buy eth with all of your money, values in the market are very unstable and you dont know what will happen to ethereum in much time, don't just trust your instincts, read and read more so that you will be more knowledgeable about ETH or whatever altcoin you will try to invest. One of the most important rules for successful investing is not to keep all eggs in one basket.