A pack of around 150 mods, it includes all the most important mods for any style of playthrough!
Mekanism, Thaumcraft, Thermal Expansion, Blood Magic, you name it, its here! For performance reasons I have avoided adding lots of small, unnecessary mods, the large ones more than make up for anything those may add. I have done my best to avoid massive overlap, such as having IndustrialCraft and Tech Reborn at the same time.
Basically you can do magic, make spells, become an eldritch wizard, study the crafts of thaumaturgy. Alternatively you can do tech, automate your riches, produce massive (and dangerous) nuclear facilities. Perhaps even combine magic and tech and become a nuclear powered wizard!
Regardless of my attempts at optimization, I still recommend the typical 6GB of allocated memory. Even that limit can be broken when loading a new singleplayer world. 8GB is the most I've ever used.