How to get a really elastic dough?

...but while it's many factored and not merely the choice of flour.  That said, my advice is to stick to white bread flour for the time being, and ignore ash content, falling number, and extraction percent.  Come back to them later.  Then study recipes and videos which focus on working with doughs with at least 65% water content as compared to total flour weight.  You must learn to make a dough which is quite full of bubbles at the end of the first rise and doesn't lose a lot of those bubbles as you are forming the loaves.  These bubbles will expand when the loaf is baked in a very hot (500 degree) oven.  To make the crust thick and crunchy, master a technique for baking you loaves with steam for at least the first 15 minutes.

All this said, while your trial and error at home will teach you a lot, it's much faster to take a course at a baking school or finding a home baker nearby to shadow while he makes the kind of bread you want to make.  Asking on this website whether there's someone in your area who know how to do these techniques might be instructive and fun.