You have far too many synergies that will obviate slowing the progression of the pack down if steps are not taken.
First off, RFTools Dimensions is a bad idea for the same reason Mystcraft was a bad idea. Once you can customize your own world, you bypass all the worldgen config settings you've set up, and have access to All The Ores. I've NEVER liked Mystcraft or Dimensions or any other dimension-generating mod for just this reason. Not talking about mods that exist within another dimension, like Dark Forest, but ones that allow you to generate custom dimensions. Besides, in spawning tons of dimensions to try and find the dimensional shards, you end up lagging out your game.
Second off, EnderIO is pretty stupidly powerful. Once Conduits are on the table (as soon as you have the Alloy Smelter and an enderpearl), there will never be another Thermal Dynamics duct built ever. While TD gates certain mechanics behind tiers of material, you get ALL that functionality right from the get-go with EnderIO. For this alone, it would get a strike in my opinion. Second, make sure you disable other mod's alloys from the Alloy Smelter, or you will find half your Thermal Expansion progression to be null and void. Especially make sure to remove Enderium, Lumium, Signalum, and anything else requiring the Magma Crucible to make. Finally, this will also make Dark Iron the go-to armor set until you hit Draconium, especially considering the Enchanter block that lets you create specific enchanting books which removes the RNG of enchanting. Which also tends to make The Ender the best sword as well. EnderIO seems to just take over any pack it is put in.
Actually Additions is mostly okay, however you're going to need to tweak some things to keep it in line. Most specifically, the lasers. You might want to jack up the cost of lasers to require Empowered crystals to keep them from obviating Ducts, and make sure there's a hefty power loss in the energy lasers so they don't just obviate fluxducts entirely.
Immersive Engineering is a lot of fun, but your'e going to want to seriously jack up the cost of the Cloche. Like, seriously. Or just disable it entirely in the configs. Otherwise, every power system will be running on this, and he'll never want to get into Extreme Reactors because he can get the same output from a single cloche.
Instead of More Overlays, just use Dynamic Surroundings, which also makes the world much cooler to be in, plus has the overlays.
Portal Gun? Really? Come on, you already have RFTools and EnderIO for 'go anywhere you want'. Is this really necessary?
Ruins is a good worldgen mod that adds in various things to your world. From broken down houses to an occasional barn-like structure to the ruins of what seems to have once been a church with a half dozen zombie spawners hidden in the pews, to vaulting spires of rock that contain a few precious ores... it's really good, and I like it.