About ketosis. Done right it can be a very effective fat burning technique. If you've seen AlteredBeast from this site he was on it at some point a while back (if I remember correctly).
While on ketosis your body will burn both protein and fat for energy. The idea here is to take in enough protein in your diet to prevent muscle loss during this. Basically you trade in carbs for protein, the extra protein gets used for energy.
Some people can mantain this with up to 30 carbs a day, some people can with only 20. One way to tell that you'r on ketosis is by your breath, the only way the body can get rid of certain ketones is through excretion through the body, so you'll breathe it out basically.
And carb intake wise it really depends person to person. If your taking in too few carbs a day, the next day your workout will feel sluggish, carbs are used to
restore the energy in your body that you'll use primarilly for weightlifting, so if you don't get enough one day you won't feel strong the next.