I think the most secure trading is to use some money from trading capital and use money that will not be in use for the near future,
for example I have $ 1000 and I need to use the money for my family's living needs, then I can use $ 250 for trading and the rest to survive, do you mean from this revelation?
this method is used so that you are not too depressed if the money you have stuck in the expensive price.
Do you have monthly salary? If yes then you can use a little part of your salary for trading. It is good because the more trading capital you have then the more profit that you can get. I suggest you to divide that $250 into to three parts, $100 for trading bitcoin and fiat pair, $100 for trading altcoin and btc pair, and $50 is for reserve fund so if you see an opportunity in bitcoin and fiat pairs or if Bitcoin price fall then you can use it to buy bitcoin at low price. Like today, bitcoin price is tend to rise , I guess it will keep rise until the end of this month.