I am planning on starting a small server for a few friends and I, we want a set of mods to make the game longer, more drawn out and definitely more difficult. Does anyone have any suggestions to make it so, without it being boring? New mobs, npcs, structures, biomes, agriculture, anything really is open, exploration and magic are pretty popular with us. Keeping us working and moving without being stuck in front of a machine grinding for hours is definitely a must.
Your best bet short term would be total immersion mods (that generally don't play well with other mods cause they change basic things about the game) like TerraFirmaCraft, BetterThanWolves, MinecraftIsTooEasy, MineFantasy, Aether2, DivineRPG and so on.