AppleSkin: Essential. It's only a client side mod but it makes the god-awful hunger system way more manageable by unhiding useful information.
Iron Chests: It's kinda video-gamey but once you've played with it enough you start to really appreciate being able to make upgraded chests out of metals.
Storage Drawers: A vanilla-esque mod which adds powerful lag-free storage (unlike coughAE2cough) capable of handing the inventory needs of modded minecraft.
Integrated Dynamics: Amazing mod which adds extremely powerful tools to any base. Make sure to install the addons, especially Integrated Tunnels.
Ding: Essential. Makes a ding when the modpack is done loading so you don't have to stare at the screen the whole time.
Gravestone Mod: Dying and losing all your stuff is complete BS. This mod fixes it without allowing people to abuse respawning.
Project E: I can't fully recommend this one, but it's amazing if you want a hybrid Survival-Creative experience. It lets you spawn in any previously deposited item as long as you can afford to. Great for a casual experience but some serious potential for world-shattering abuse and not even remotely balanced for survival gameplay.
Recurrent Complex: It adds fun dungeons you can raid. The worldgen can get a bit much, but I think the fun of raiding their structures makes up for it.
Extreme Reactors: If you're going to go the route of Project E, you may as well go all the way with the ridiculous power output this mod provides. Will you ever need that much power? No, no you wont, but you will have fun designing reactor chambers that both fit within your base, fulfil your base's needs, run reasonably efficient, and not break the bank in the process. I would suggest turning the configs WAY down if you want to include this in a normal pack.
Nuclearcraft: The far-more balanced and realistic alternative to Extreme Reactors. It's a little heavy and kind of gets in your face a bit, but solving the complex uranium chain is extremely rewarding.
Antique Altus: Extremely lightweight mod which adds a beautiful auto-map.
Pneumaticcraft: It's fun, it's lightweight, it's content. You get to be iron man.
Open Computers: Lightweight mod which adds a crap ton of content. Also has a lot of phenomenal add-ons which add even more content.
OpenSecurity: Opencomputers addon which allows players to protect their privates using various things such as biometrics and keycard readers.
Computronics: Phenomenal addon for Opencomputers which adds all sorts of extremely interesting and powerful mechanics, such as the ability to play real audio streams. Yes, you can stream actual waveform audio.
Cooking for Blockheads: Essential. Adds a system which improves the heck out of Pams Harvestcraft microcrafting and adds some nice-looking and useful blocks as well.
Modular Powersuits: As fun is it is unbalanced, which is to say, extremely. You can do some aggressive tweaking in the configs to make it balanced (ask me, I have a really good config if you want it) or just enjoy the broken. At a minimum disable the kinetic generator because that thing is not OK. You can run your entire base by running in circles.
Nutrition: Sorry, no link because I can't find it, but Nutrition is a better take on Spice of Life. Just remove Spice IMO it doesn't add anything.
Logistics Pipes: This one is a risky add on smaller servers because it can cause lag issues, but the stuff you can do with it is beyond galactic. Essential if your server can handle it. Use ProjectRedTransportation if it can't.
Fat Cats: OK I have literally never heard of this mod before but I think we can all see the potential here.
NoDamageI: Another one I couldn't find a link to. You know how mobs go invincible after you hit them? Really sucks the fun out of rapid-fire weapons. Remove I-Frames from all mobs and optionally players as well.
Albedo: Great mod left in obscurity due to its awful name. Adds real Colored Light support to the game, adding a whole new dimension to building. Might be laggy for some. Tends to crash with certain mods. Be sure to include addons because this mod does very little on its own.
Rockhounding: Haven't tried this one but it seems to be a spiritual successor of Minechem, and Minechem was awesome.
Sign Edit: Essential and literally a couple lines of code.
Kinda considering putting Avaritia in here. It's ridiculous and doesn't take itself seriously, at all. Completely pointless mod, and that's the point. Seems to have a lot of addons too.
Nether Ores: Gives the nether a reason to exist.
OpenPeripheral: It's only on 1.7.10 but I'm sure an updated equivalent of this exists somewhere; It adds "terminal glasses" which allows you to draw custom HUDs on your screen, AR-style. It's really cool.
Remove Mousetweaks because it's awful and can sometimes delete items (players who want it can still use it as it's client-sided) and Quark because it adds almost nothing and the dev for it is a reactionary.
If you got any questions feel free to ask. I do a lot of pack dev so I have a crap ton of experience with this sort of thing.
A lot of the mods I listed here are also on 1.16.5 You can use Curseforge to search mods and also download them which helps a ton in building your pack.
Best tech mods IMO are Immersive Engineering, Ticon, and maybe Mekanism. Thermal Expansion/Ender IO are fine but really overrated, and IC2 is fun and enjoyable but really badly designed. There's a couple great obscure tech mods out there if you're willing to do a little pioneering, though they usually take a little bit of extra CraftTweaker-ing to fit in nicely with the rest of your pack. I always personally enjoyed Pneumaticraft the most but I feel like it's more of a support mod than something you can build a pack around, which is great because it can safely fit into pretty much any pack anyway.
The most important thing in building a pack is maximizing the amount of things your community can do while minimizing bloat, complexity, and load time. You want people to have the tools to make their own fun instead of just railroading them down a pre-defined progression like some packs, or just throwing everything at them all at once with no consideration of balance and overwhelming them like most packs.
Pack is really light, you should add the following mods:
Remove Mousetweaks because it's awful and can sometimes delete items (players who want it can still use it as it's client-sided) and Quark because it adds almost nothing and the dev for it is a reactionary.
If you got any questions feel free to ask. I do a lot of pack dev so I have a crap ton of experience with this sort of thing.
deleted by creator
A lot of the mods I listed here are also on 1.16.5 You can use Curseforge to search mods and also download them which helps a ton in building your pack.
Best tech mods IMO are Immersive Engineering, Ticon, and maybe Mekanism. Thermal Expansion/Ender IO are fine but really overrated, and IC2 is fun and enjoyable but really badly designed. There's a couple great obscure tech mods out there if you're willing to do a little pioneering, though they usually take a little bit of extra CraftTweaker-ing to fit in nicely with the rest of your pack. I always personally enjoyed Pneumaticraft the most but I feel like it's more of a support mod than something you can build a pack around, which is great because it can safely fit into pretty much any pack anyway.
The most important thing in building a pack is maximizing the amount of things your community can do while minimizing bloat, complexity, and load time. You want people to have the tools to make their own fun instead of just railroading them down a pre-defined progression like some packs, or just throwing everything at them all at once with no consideration of balance and overwhelming them like most packs.