This will only be reasonable if you plan to make a good detailed campaign with good plot. If you're planning to make something as simple as PB2 campaign but with 2.5D effect and some extra small things, then just ignore this.
Step 1: you hire the most talanted community team to make the campaign for you (for free, don't pay them). Twenty hands are better than two. You give them the script, explain your vision of how maps should look like, and control their work while chilling at the beach (joke).
Step 2: you don't make 100 levels. The main purpose of the campaign is to show game features, give newcomers a good first impression of the game to make them stay in your game forever and maybe make maps (because map making is the only reason why PB2 lived for more than 10 years). What about 12 big well detailed levels? Should be enough to finish the plot since it's not too deep anyway. Okay, there can be more if you want. Maybe 15?
Step 3: if you want to make lots of levels (over 9000) you make the campaign seasonal. Make the first part of the story now, release the game, then finish the campaign later by publishing packs of maps (season 2 maps, season 3 maps, season ...). Each season will be one small finished story which is the part of global story (plot). It would save the time for you and perhaps motivate you to add alternative stories in future. It would also keep the people hyped which is good.
PROFIT. You saved a lot of your time and nerves, have a great looking campaign you can be proud of, and released the game earlier (not in 2032).
>>>Pls send to Eric, thx<<<