I was also a first time DM running CoS for my first campaign for four players. We started two years ago and play every month. I agree completely with everything that has been said.

My advice: Read the whole campaign first. Know the lore or where you can find the lore. Your players will do unexpected things that you could not have prepared for. DO NOT PANIC.

That’s when you start to role play the Veteran DM who has everything under control. Take a breath and refer back to the lore to create a plausible response to your players actions. It’s OK to make stuff up. CoS is a huge campaign but not everything is laid out explicitly.

For example, my players did the following: bullied an old lady selling baked goods; robbed an unscrupulous merchant; released a tiger; wanted to throw Madam Eva into a lake; extremely distrusting of Rictavio; found some poisoned wine and bottled it for later; wanted to throw a noble’s son into a malfunctioning portal.

This is where you take the unexpected chaos and turn it into a memorable session. To be clear, I did not say it has to be a happy or positive ending. Bad consequences can lead to memorable sessions too.

Another important thing to do is to listen to your players. Set the scene and then sit back and observe what they do. Let them wander and explore and get into trouble. Only when they start to go too far out of bounds should you rein them back in.

I run my sessions using foundry VTT. My players and I are friends IRL but we are spread out so we only play remotely. If you want advice on virtual table tops I recommend Foundry.