Yes, unless your SaaS deals with life and death or 99.999% uptime contract, you're pretty safe running something like Django+Redis+Postgres+NGINX in a single bo

Yes, unless your SaaS deals with life and death or 99.999% uptime contract, you're pretty safe running something like Django+Redis+Postgres+NGINX in a single box for years and sleeping well... once you hit some really big number of users you might want to change it a bit and hire some people.