Is it OK to add flour when I first mix the dough to get it to the right moisture level and consistency?
I feel like I should add a bit more flour so the dough is not quite as wet, so I can give it the tension it needs when I shape it, or do I need to get the moisture right from the start?
No and yes... Adding flour to get the "right" consistency is not really the point. The point is to get the hydration just how you want it in the first place, because by adding flour you are changing the recipe and therefore changing the hydration rate which makes the recipe redundant.
A wetter dough will bring different characteristics to the bread. There is no point making a wet dough to get a specific texture of bread, and then adding flour to make the consistency manageable, because then it's not a wet dough anymore and you lose the characteristics.
I never add additional flour, and only dust where necessary during the shaping stage.
If you are struggling with a wet dough here's what I would do... First do some bread maths to work out the hydration of your recipe. (This video will help)
Then, instead of adding flour, remove some of the moisture from the recipe to make it the manageable dough that you are comfortable handling. Yes, it will still change the recipe but in a much more controllable way. Write down what you did, how you found handling the dough, and how the bread was in the end.
Next time around, crank up the hydration a touch. Get the feel of the wetter dough and see how you feel about it. Keep upping the moisture each time you make one. Then after enough practice you'll be able to handle a wet dough like a pro, or at least you’ll discover the level you are comfortable with.
Here’s a tip: If your dough turns out too wet to shape up, cut your losses and make the best focaccia you’ve ever eaten!