this will be different for every people because we don't have the same goals in trading and besides that, we need to determine how much profit we want to take in every day. I think maybe for me, 1 btc is enough to start day trading and we can reach much of profit with that amount but maybe less than 1 btc and more than 0.3 btc it is enough to trade. and if you want to make a big profit, I think you should have a big capital too so when you buy the coins at a low price, you can sell it at the high price to make a profit.