As a person who helps part-time at my buddy's winery... fermenting apple juice is a hangover waiting to happen. Depending on the batch of apples (they vary a lot), it can come out cloudy, due to pectin breaking down during ferment -- not toxic, and can be filtered out (coffee filter should work). Or adding pectinase to the apple juice will smooth out the pectin.
And make sure to use apple juice that doesn't have any/much preservatives -- they keep the yeast from growing.
I believe typical apple juice is about 10-12% sugars. If you're looking to get schnockered, most wine yeasts can ferment up to 25% (give or take), which by my shaky math, mean one could theoretically add about an ounce of sugar per 8oz of juice, and keep upping your ABV%. Ferments can go to about 16-17% alcohol before they die off.
Disclaimer -- use this advice at your own risk. I hold no responsibility for any ill effects on anyone's health.