Yes, I believe ash would add flavor. I'm pretty sure it's a flavor that could be done without. As far as the sticking part is concerned, it works the same as a piece of meat on a grill; initially the dough will stick, but after a minute or so of baking it will move around all you want.
Back to the placement question, now. No matter where you have the fire, it will take up the same amount of space. Yes if it's on the side you can't load pizzas into the fire. If it's in the back, same thing. As far as the wood burning faster in the back. I'd venture a guess that this is not true. Fire needs air to burn faster and I'd be willing to bet there is more air circulating through a fire built on the side (where it is closer to the flue) than in the back.
Aquote from Woodstone, the manufacurers of the most popular type of wood-fired ovens in the U.S.A: " The oven is heated more evenly and effectively by the fire positioned on the side rather than in the rear of the oven." Click here
for complete article.