What is a decent amount of Bitcoin you should have to make day trading worth while?
it's totally up to you. low invest means low profit and also low risk. so i think it is wise to start with low amount for beginners so when you feel confident then you can increase your amount.
But low profit isn't worth with your time , talents and efforts you did spend on it, right?
Why not keep holding your bitcoins, go and do the research on your own. I always prefer reinvesting into potential altcoins rather than trading.