It took longer than I thought it would, but I finally finished my modpack.
The title is tongue in cheek. What really makes a modpack "expert" anyway? This pack has a lot of custom recipes, but no forced progression. There are four main mods, Immersive Engineering, Ender IO, Botania, and Astral Sorcery. You can start with any mod you want, but will have to go through all four mods to complete the pack to craft creative items (using Extended Crafting). Other mods are included, but I disabled certain machines to avoid redundancy.
The other main change I made is that there is no natural ore gen, except for the Beneath. You are going to have to sieve for resources using Ex Nihilio. Later, you can mine in the Beneath, use Mystical Agriculture, or Environmental Tech. Of course, you can also use the ore gen methods of Botania, Immersive Engineering and Astral Sorcery.
Roguelike Dungeons have custom loot in them. This is what took the longest time to figure out. There are also several mods to help with building and base decoration, including Chisel, Chisel and Bits, and LittleTiles. Also, there is a quest book to help achieve your goals and focus on what to work on next. This isn't a tutorial modpack and there are not 100s of quests, just the main items you should be focusing on. There are no random loot chests; most rewards you will have to chose what you want from a list.