How to make my pizza dough Soft?
If you've added 250ml of milk for 1.5KG of flour then your dough is way too dry, there isn't nearly enough moisture for any kind of bread dough. A typical traditional pizza base recipe uses a ratio of about 5:3 flour to liquid by weight, meaning you'd need about 900ml of liquid for the dough. You've also added milk powder, which also needs to be hydrated, so add about 30ml or so for that as well. If you are using all purpose (plain) flour you should add a bit less water, say 10%, as there's less gluten in it.

When you add the liquid to the flour it's going to be sticky, very sticky in fact, but that's bread making and you can't avoid it. You can oil your hands but that doesn't last, you're better off removing your rings and just cleaning your hands later. As the water incorporates and is absorbed the dough will get less sticky, but pizza dough is going to stay a bit sticky even after it's been kneaded enough, it will then be much less sticky after the first rise.

The recipe you have isn't any kind of pizza base recipe I've ever heard of, milk, milk powder, eggs and sugar are all enriching agents and the dough you'll get isn't going to have the kind of structure you're looking for in a pizza base unless you're looking for some sort of non-traditional brioche style. It's also going to take much longer to rise as these ingredients slow the process. Traditionally a pizza base is flour, water, yeast and salt with olive oil being optional (I put it in).