Trading in altcoins can be started even at 0.001btc but that kind of trading doesnt worth any think,the minimum amount i say should be 0.25btc reserved for that.Its not neccessary to use them all at once,must that much must be in reserve.
even with 0.001 bitcoin you can make a good profit out of it if you can manage to always get profit,it's indeed will be cut off by the fees but only small percents so it's not going to be a problem,it's worth trying to be honest