"If Mercer can do it, so can I!"

Famous last words.

My first DnD group was a whopping 12 people and honestly, I don't know how I still fell in love with the game because of it.

My first ever campaign I ran was lost mines. The first session we had 4 players. It went very well. After a while people started asking to join and by session 5 we had 8 people. We finished the campaign but it made me consider never dming again. Im glad I tried again later with a smaller group but 8 player sessions exhausted me.

Also worth noting...many of the "huge" D&D groups tend to be a headstrong DM who's trying to impress people...while the players are only loosely engaged, and just "going along" with the game, rather than being active in it.

The biggest mistake new DMs make (actually, even many old DMs) is trying to write a story. The story is what happens at the table, not what the DM plans or what the module says. It's a very subtle but important distinction. As a DM, you should never assume that events will unfold in a certain way. Just set up situations, understand the motivations of the NPCs involved, and remember that players have access to magical and mundane ways to circumvent most obstacles.

Having run a campaign for 3-4 players... when 1 or 2 routinely "can't make it", it basically means session's canceled. A larger group, with all of its scheduling conflicts and other issues, can potentially allow you to run your session since there are more people attending.

The real biggest mistake new DMs make is- creating your own world. Dont. Pick a tried and true starter adventure, run it- then start your own world, Learn how to DM, then invent a world.

Here's a trick from 2nd Edition: session zero. When everyone comes in, have one copy of the Players guide, and everyone makes their character then and there with the intent of everyonemaking a character by session's end.

The social dynamic will start to show itself rather quickly. It's a team-oriented exercise which also shows how well people can share the spotlight (represented by the book). If you have to scrape up another PHB, then chances are the group is too big, someone might need extra attention,  or is busy hogging "the spotlight".

I’ve been DMing a group of 7 for several years now. It was a learning curve at first for us all, but we’re all best friends and family and we’ve learnt how to overcome the problems mentioned in this video.

We have an amazing time playing and hanging out and the table never gets stale or boring with the 7 of them. It can be done! ❤

"If Mercer can do it, so can I" is an okay-ish assumption, "if an on-line entertainment show can do it, so can my regular campaign" very much not.

I like to run tables of five.  Here is why, if one player ends up not making it, I can still run my session.  Where if I have a table of four and one player does not make it, then most of the time the session ends up getting cancelled.  This is mostly because I run a very tight challenge with most of my combat's and it is much easier for me to adjust down to four than to three.  For some reason adjusting to three seems to be more difficult.  But this is just what I have encountered.

I totally agree with Kelly and Monty on this.  I'm a moderately experienced DM, and I currently run 3 campaigns, two have 4 players, and one has 6.  I find the session with 6 players SO much harder, and SO much more exhausting.  There are a couple of quiet players, and I seem to spend half the evening trying to draw them into play, quietening the extroverts so the introverts can say something.  Maybe it's just the people in the group - well, no.  Because both quiet players and one of the extroverts are also present in one or other of the 4-person games I DM.  In those campaigns, with less people in the room, they seem much more able to contribute easily, and I can concentrate completely on DMing the campaign, rather than having half my mind taken up with managing the social aspects of a 7 person table.

I’ve played 5e for several years now, and my DM has always managed to comfortably run tables of 5-8 players. The worst was when he had to DM a table of 13(!!!) players at a LGS because the other paid DMs did no-shows. Now I’m running my own campaign for the first time with 5 players, and I’m loving it! I plan to also run a oneshot in the near future with 4 players to see how it feels.

I insist that I won't run a game for more than 5 players and even 5 is too many to be ideal, but it is just about manageable.
My sweet spot is 3 or 4 players, I think that's the easiest to 'balance' and ensure everybody gets some spotlight while still having enough folks for fun group dynamics.

Totally agree with the player number issue. I started DM'ing after watching CR, because I wanted to play DnD and at that time there were no people around, even playing. I started with 5 players, by the second session there were 8. Total mess, endless combats, had to split the group.
Later I started a weekly group with people I met through facebook and became really good friends with them. I DM'ed for them, too and at the peak we had 7 Players. Combat IS the biggest issue in my opinion, just as you described. We made it somehow, now we are in our second homebrew campaign, usually with 5 players at one time, due to scheduling issues, and it's much easier to run.

Listening to the pizza analogies while eating a pizza :)

It's a very big big mistake that not backing Monsters of Drakkenheim with the current Kickstarter 🙂

My first time DMing was for one person with an original one shot and I learned a lot about how I like to run my games and what does/doesn't work. Now I'm running a game for two and everything feels natural and fun, I get to shine the spotlight on both of them equally which leads to a really personal and awesome experience!

I'm so glad that I did many of the things you recommend here.  I haven't DMed for 25-30 years, so I asked my bestie (who gamed with me way back then) if she was interested in a weekday morning game while the kids are at school.  Then we thought about who else might want to play with us and we picked my college daughter who has no classes that morning, and a self-employed friend of mine who has a flexible schedule.  So it is just the four of us (ages 48, 47, 20, and 39, from two states) and once we took two sessions to figure out all the tech aspects of playing on Roll20, we finally had our first actual game play the other day.  Our plan is to run a few sessions until college is out in mid-May, then evaluate what we want to do.  If all goes well, my daughter's summer job will leave her free still at that time slot and we can keep going.

You definitely need to do mini campaigns with people. If I'm considering someone for long-term, I will have them hop in as a guest for a 2-3 session arc in the campaign, without mentioning that I'm looking for someone to join on a long term basis. I hate being in a situation where I have to tell someone they need to leave the campaign, so avoiding that conversation by doing some thorough scouting is important.