Running battles offline

I’m planning to run storm kings thunder for the first time soon (first module campaign also) but I’m a bit taken aback by the size of the level 5 city encounters. I usually run battles on a battlemat (offline) but most of the examples I’ve seen of people running these encounters have them using online services like roll20. Do I just pick a small area of the town where all the combat will take place? Erase everything as the players move around? Scale everything up? I also feel like these combats have a few too many creatures and will likely get boring quickly with a semi large group of players. Has anyone else run through this offline and is willing to share with me their experience?