New DM campaign planning

[Mandarin]

Alright so I will be DMing for the first time in about 2 weeks and wanted to get some feedback into my master plan since I am hoping this campaign will be going on for a few years.

I will be doing the mines of phandelvar module from the D&D starter set to begin with. I dont have it yet should be arriving this friday so I can start preparing. Group will be about 5 pc's. Most are new to either D&D or just 5e. They havent decided classes yet. I am starting with a module to get my dming feet under me and have some support until I get past the learning curve.... but I have a master plan in mind that I need help with.

Somewhere in the mines I plan on introducing some sort of underground entrance that looks to be an ancient civilization with building abilities surpassing even the dwarves....

Once the mines of phandelvar module comes to a close I plan on introducing some sort of worldwide apocalypse that forces the heroes and surrounding towns underground into said underground complex for the next 100 years while this cursed apocalypse happens... Obviously this complex is going to be thousands of miles vast and hundreds of miles deep.

I plan on doing a sort of zombie apocalypse on the surface... anytime they get close enough to the surface they start running into skeletons and zombies that transmit diseases.Underground there will be sections of giant mushroom forests for miles and miles and lichen that light up the underdark in different color hues.... Giant underground cities... some occupied... some abandoned... massive underground lakes... ancient treasures long forgotten... and ancient foes long vanquished that were never truly gone but just waiting under the surface.... you get the idea though... vast and diverse... I really want to take advantage of the giant mushroom forests and lichen that glows.

So here is the plot.... heroes and surrounding towns are forced underground... (About 200 people) they only have about a months supply of food and water with them and need to find safety. Heroes first forays are finding safe dwelling place for so many and eventually find an ancient underground city that is defensible, has a water source, and even viable food via fishing and underground flora.... but the city has to be cleared out.... while clearing out they find a patrol of goblins.

Over the course of several months they clear out everything, get the town going and even start getting townspeople doing patrols and capable of defending their own town all the while running into various underground monsters and whatnot. They also find a strange magical portal in the city that a friendly sage tells them he believes will teleport them to any other teleporter they have visited before as long as they have attuned to it.

Eventually I want the heroes to be forced to leave on an epic quest to discover and save other people forced underground and to save civilization itself by approaching the source of the apocalypse from underground, maybe to find it was the work of an ancient black dragon and some ancient sorcerer of an unknown race... I dont know yet but you get the jist.

So what do you guys think? Any tips on races and monsters they might find underground and there I could get their stats? Fun plot hooks? General advice?

[Mandarin]

Also, I plan on really taking advantage of puzzles and riddles as they progress.... for instance the portal room might be sealed and in order to access it there may be a puzzle or riddle involved in order to gain access... that sort of thing.

I am pretty darn good at improv and adding things as I go but I am trying to build a general gameplan and also as much specificity as possible. <3

[Freemason Than]

Baby steps.

Focus on the module you're going to run first, rather than mapping out the entire campaign after that from start to finish.
Especially since this is your first time DM'ing.

Make sure your players get a good experience right now instead of all the hypotheticals of a future campaign that may never even come to pass.

[Moosoculars]

I always think that it is good to have a grand plan in the background to inspire you. However with your idea I do see some issues

1) Your apocalypse setting limits the world in which the PCs can interact. For example there is now no trade, no economy, no port cities, a lack of information, spellcasters, magic, no forests with elven cities (mostly destroyed). While all of these things can be created and added they will be the exception and not the rule. How do you get basic spell components now you are stuck underground?

2) you may nerf a number of characters to the detriment of their fun. If you have a Forest Ranger now stuck underground or a druid who will never see any other animal to wild shape into.

I agree that if you are new to DMing that you should focus on the basics first. But if you do run the apocalypse setting you should have a way (or ways) that the disaster can be stopped i.e. one win scenario.

[Celcey]

Rule number one of DMing: no plan survives first contact with the PCs. Never plan on what they'll do, because they won't, and if you have a specific idea that you want and they don't do it, that won't work. Remember, you're not writing the story, you're guiding it.

Also, while the setting is a cool idea, and maybe something to work into an overarching plot line (if they fail to stop evil x, z-day arrives), it does restrict a lot of other cool stuff. More importantly, it's a very specific setting, and the players need to both be aware and okay with that. It's important for their build information (like a land Druid might want to go Underdark, or someone may decide to play a drow), and because it's a specific genre of game, it's important to recognize that there may be people who don't want to play an apocalypse game. Talking to your players first is very important, especially if y'all are new to any of this stuff (edition, game, DMing, etc).

[Mandarin]

All great points...

I dont really require specific spell components from players and would just require the GP worth and a vendor will be made available for components whenever they are in a town.

I was also planning on the PC's finding whole civilizations that had seeked refuge underground... wood elves would now be living in the giant mushroom forests, ect... and who is to say there would not be port cities for underground oceans? I mean all of humanity had to either flee to the underdark or be anniahlated... but in a magical world they could have transported whole cities underground.

I would also allow for certain changes to be made if it was gimping a class... I also plan on telling the PC's before their character creation that they will be spending a lot of time underground and to create their class/spell list accordingly.

And I totally plan on investing the lions share of my time to the current campaign and ensuring they have a great time... I just dont have the module in hand yet so wanted to brain storm my ideas and see what issues people see arising and make sure I am ready to address them.

[Gastronomie]

The Out of the Abyss module features quite a lot of interesting underground mushrooms, including edible ones, poisonous ones, and even one that makes your body enlarge when you eat it (1 UP!!). And it also gives you some ideas for underground encounters. You should give it a read - or you might even feel like running the module once you start reading it (you could easily connect Phandelver to Out of the Abyss by saying that the Black Spider was working for the drow, which is not really much of a surprise since he's a drow himself).

[Shining Wrath]

You have the framework of a campaign, and that's good. You'll have several sessions while they work through LMoP, and there are places therein where finding a sealed entrance to the Underdark will work, so you'll have time to develop your ideas.

I think you need two things first: the initial "base town", and the final Big Bad Evil Guy or Gal. Work from the base town out; the BBEG is not immediately on stage, but start thinking about what sorts of minions would be appropriate for level 4 / level 5 characters to encounter that would "point the way" toward the eventual dramatic confrontation with Ultimate Evil.

Also, you may want to change some of the rooms in the Mine such that it would be worth the risk for the party to go back to the Mine occasionally.