Alex,
I think it is a good idea for a beginning pizza maker to weight the flour and water. Doing this, especially with a proven recipe, will get you get more accurate results to begin with. You didn't indicate how you calculated the 50% hydration number but if you were using a proven recipe and a scale, the dough shouldn't have been sticky and impossible to knead at 50% hydration. Most 00 flours are rated at around 55-57% hydration and some can tolerate over 60%. If you used volume measurements and guessed at the hydration, then it would be easy for you to be far off on the hydration.
Usually, bread machine yeast, at least in the U.S., is IDY or something tantamount to it. However, many bread machines call for ADY. Just looking at the numbers you provided, I would guess that you have ADY. The 7-gram packet is equal to 7/28.35 = 0.25 ounces. In the U.S. that's equivalent to 1/2 ounce fresh yeast. To be on the safe side, you should look at the instructions on the packet of yeast. Typically the instructions for ADY will say to either rehydrate the yeast in warm water (110-115 degrees F in the U.S.) or mix the yeast in half of the flour and other ingredients and use much warmer water (120-130 degrees F). The instructions for IDY will usually say to just mix the IDY in with the flour, not water. I would go with the instructions on the yeast packet. If in doubt, you can always rehydrate the yeast in water, even if it turns out that what you have is IDY.
As for the knead times, that will depend on the dough batch size. A bigger dough batch size will take longer to mix and knead than a small dough batch size. I suggest that you do the following for a hand knead: put all of the water into the bowl, add the salt, and stir with a wooden spoon until the salt is completely dissolved and you can no longer see the grains of salt (about 1 minute); add the yeast to the flour if IDY, or add previously-hydrated ADY to the water/salt mixture in the bowl; gradually add the flour to the water in the bowl and stir using the wooden spoon; at the point where using the spoon can no longer easily move the dough, remove the dough from the bowl and put onto a lightly floured work surface; put the remaining flour on the work surface and gradually work it into the dough, little by little, by kneading until the dough takes on a smooth appearance and feel. Ideally it should be on the slightly tacky side, however, it is still possible to tweak the ingredients by adding more flour and/or water. If you are using a proven recipe and you weigh the flour and water, you shouldn't need more than say, a teaspoon of either flour or water at this point.
What I have found useful in hand kneading doughs, especially those using a high-gluten flour (which the 00 flour is not), is to use an autolyse-like rest period during the preparation of the dough. In the above sequence of steps I outlined, I would introduce the rest period just after a good part of the flour has been added to the water/salt mixture in the bowl and mixed with the spoon. Just cover the bowl with a towel or sheet of plastic wrap and let it sit for the duration of the rest period. If you are only making a single dough ball, I would use 5-10 minutes for the rest period. If you are making several dough balls, I would use 20-25 minutes. I think you will find that the rest period will make the kneading go much easier.
Peter
