How do I knead this dough by hand?
Ciabatta is usually a fairly high hydration dough.  You probably won't be kneading as you are thinking.  You can use the "slap and fold" method to build the gluten network.  There are plenty of videos illustrating the technique, just google.  Basically, dump onto counter top.  With a hand on either side, lift and pull the dough toward you.  The end farthest away should stick to the counter.  Stretch but don't tear.  Quickly flip the side in your hands onto the dough, essentially folding it in half, and trapping air.  With both hands, lift the mass, flip it over, slap it back down, and repeat.