Need opinion/help with new campaign

[Lloyd-Starbuck]

So i'm going to be the new DM for my group in the near future (about month) and have been reading the DM handbook. I also have help from my friend and brother (both DMs).I'm tying to make a campaign without them knowing what is, so i can't ask for help from them, so I would like your guys opinion and on the campaign I have working on.

1. the campaign will start off in a city and the players will be part of a guild. my plan is for each session there will be a quest board in the guild hall that will have a couple of different quest on it ranging from different levels. I'm doing this because the group that I play D&D with has a had time focusing on long term quests, so these will be short term quest that they can chose and change at any time. Does this sound like a good or bad idea.

2. this is a optional idea, but some of the players also have a hard time sticking to a single character idea.
so my idea was that after a mission if they did not what to play their characters anymore, they would be able to switch to another character from the guild. I want this to be only if they don't like their character anymore.
The problem with this is that I feel that they would not be dedicated to their characters and constantly switching. how can I prevent them from doing this all the time without penalizing them.

3. any tips will be nice.

[Geddy2112]

I am currently playing in a campaign exactly like this. We are part of a guild in a giant underwater city similar to Rapture from Bioshock minus the dystopian aspect. It is tons of fun, and despite the fact that we built this to have a fun puzzle/combat heavy module where we could try various builds, we have had a lot of roleplaying and storyline. It is a great idea and tons of fun. We have not had any characters switch, but we are free to do so if we choose. This is the kind of game that helps people figure out the mechanics of a system as well as what they like to play. Better to roll up a "just for fun" character in a story light campaign and like it than invest seriously into a concept and end up hating it two sessions into a major roleplay campaign. Don't penalize players for switching; I doubt players will want to switch every session. Another way to cater to switching is make high lethality encounters.

A few things I have liked:
Have an overarching plot. Don't just have a static world where nothing happens. Not every guild mission has to be tied into the story, but make a few have major impacts in the world. Perhaps accepting one mission and not another could lead to a major change for the future.

Have varying challenge levels. Normally we have 3 a session, one is ECL=Party, then ECL=Party+1, then ECL=Party+2 or +3. Or something along those lines.

Have optional parts to missions and multiple ways to solve them.

Make mundane tasks into dangerous missions. Better at lower levels without powerful magic, but something as simple as fixing a gas leak or welding can be a challenge in the right scenario. Adventures go after monsters for money and treasure, but a non combat style encounter can still be lucrative.

[Karl Aegis]

It's a serialized campaign. As long as failure leads to something different than success your scenarios should be fine.