The data will be stored the same whether you use a glide table or a google sheet. The only difference between the two is that there is the extra step of the data having to sync between glide and google. They both function the same otherwise. The only time I use google sheets, is when I need the data in the Google sheet to work with it in a way that I can’t when it’s in a glide table.
All data for everyone will store in the same table. I would make sure you have an email column in the data, so you have a way to know which row belongs to each user. Then you can simply filter the data by signed user (less secure), or apply row owners to that email column (more secure). If you don’t use row owners, then all data is downloaded to each user’s device. You can filter it, but it’s all still on the device and accessible to those that know how to access it. Row Owners is more secure because only the rows that a user owns are downloaded to their device. It all comes down to how secure the data needs to be. There’s advantages and disadvantages to using filters vs row owners.