Answer 1

Using caching, rabbitmq because it is fast and docker for fault tolerance. Docker Is really good because if a part develope fault, other container still work.
If there are many users, then we use many storages for database so indexing can be fast. My English is not good

Answer 2

U could use bit masks it saves lots of space and time like user roles or any additional benefits that your website serve to user in addition try to use multi threading with database for fast search and caching is a big deal. hope that can help u :')