From someone that has done mods after putting 1200 hours in the game: first runs are better with only some QoL and maybe extra graphic mods, like the extra hallway/room background, the better translation and better skill descriptions one.
Then after a run where you reached at least rank 5/6 heroes, do one with some extra class mods, start with the Marvin Seo (that has worked with the creators of the game) ones and maybe some other balanced ones (like the Milkmaid and Beastmaster).
Then the insanity will start when you see how many mods of any genre exists - from extra dungeons/zones (like the Islands), to any type of hero you can think (including cute anime girls), to new Bosses, to complete reskin of basically everything.
And then you install the no vanilla mods, and begins doing only-mod-heroes runs with everything reskinned as cute anime girls.