The 24 Storm Shield Defence Missions in the Main Questline will reward you with 100 V-Bucks for each mission. However, these 24 V-Buck missions are buried under 208 total quests*.

But while doing the Main Quests you will automatically receive V-Bucks from other sources like Challenges, Daily Quests, Timed Quests, Collection Book and the Login Rewards.

208 Quests- 4 Areas

Save The World has 4 different Main Quest areas. Each area has 6 Storm Shield Defence Missions with the 100 V-Bucks as a reward. Progress will be the easiest in the beginner zones (0-30). From then the quests will take longer and get more challenging.

To complete all Main Quests it will take most likely over 60+ hours. If you manage to get to play with higher level players, you will get faster progress. However, you may come across many games with leavers and players who are afk or just not good at the game. This can get frustrating, so I recommend to find friends in the game who have the same or a higher power level than you.

*The number of quests can vary from patch to patch.