Yes. With the first DLC you can do the Master Trials once you get the Master Sword. Both of the DLC's add so many chests around the places not far from the Great plateau. As soon as you get off of the Great Plateau there is so many treasure chest that you can find. But some of them are far from the Great Plateau. But you don't have to beat the game to get a lot of OP armor. And I'd say that after you beat the game normally you should do the rest of the DLC.
Also, you can play on a Master Mode version of your save file making the game a lot harder.
I'd say that after you beat the Great Plateau head to the Coliseum of Death and get some nice loot from chests in the ground there. Oh ya, all of the DLC chests are hidden in the ground. To find them after you beat your first shrine outside of the Great Plateau you will get quests that will tell you where to find books that will give you clues about where to find them.
I think that you should get Majora's Mask as soon as you can from one of the chests, as it makes all monsters think that you are one of them. I used that so much during my play through of the game.
So yes, you can do lots of DLC stuff without beating the game. As a matter of fact, all of it can be done without beating the game! That is since for the Champion's Ballet DLC after you beat all four Devin Beasts, not beat Ganon, you can do the Champion's Ballet.