Just set aside 500 dollars a month and when you have 5k you just wait till bitcoin drops down and buy 1 with that 1 bitcoin you invest in other coins and make the most out of them that is what i did and i have a lot of profit out of them.
You really have a good plan, just set aside an amount of money and wait for the right time to invest into bitcoin and altcoins. As of now, I will advise to invest on Altcoins cause they will rise very soon in price rate, especially Ethereum.
For bitcoin, this is not the right time, the price is still dropping slowly and very soon it will drop to a very low rate and will get pumped again. So wait for it to drop and invest immediately.