I wouldn't recommend constraining yourself to building whatever is the "most efficient" in an absolute sense.
Not every mod author has the same sense of game balance. While the modpack creators do make an effort to exclude super cheaty "dirt to diamonds" type mods, they do wind up accepting a wide variety of mods, since the interesting mods out there come in such a wide variety of flavors.
If someone were to do research and prove that using turtles with such and such a pre-packaged downloaded mining program was the fastest way to get to X number of diamonds early game, it would not necessarily follow that doing things in exactly this way will result in the most enjoyment for you as a player.
Rather than go out of your way to find the most optimized path, I would recommend instead that you think about what things you would like to accomplish, investigate the options for what mods can help you fulfill your goals, and pick whatever path of mods and tasks sounds like it would be the most fun for you. Sometimes finding your own way can be more enjoyable than following a canned path, especially if you are learning mods along the way that are new to you.
Have a look at the spreadsheet in my sig to help you sort out what tasks you would like to set as goals for yourself, and what mods you would like to try out to help you accomplish those tasks. If you then come back here and post that you have decided to work on doing such and such, and what mods you want to try out, then maybe folks can give you more focused, constructive advice on how to efficiently accomplish those specific goals.