So DLC is necesary to grind? Do I need it on Hard? I don't want to support DLC, the game has enough content by itself
Try to go for a no grind run, for the classic FE experience.
Also the only games where I would not support DLC are those that do not have enough content: "so you developed a incomplete game and want me to buy extra to compelte it? nope". I really really recommend the Future Past dlc, is amazing and along with the Scramble pack they add a lot to the game.
Future Past:
In a alternate future, the parents are long dead and 12 children just got the gemstones and the Fire Emblem, but every group is in danger of being killed before getting together to perform the awakening. Just like Lucina in the main campaing traveled back to help you, now you travel to this doomed future to help the children and save their world.
Also, about future past (for those who finished the 3 chapters)
Even though the game says this future is like the worst possible future, they actually got the Gemstones unlike Lucina's future (they could not find all the gemstones). Which means Lucina and co left a completly doomed future behind while the FuturePast crew still have the chance to save theirs.