1. First off, don't think too much about what programming language/framework to use. For such a user base you can use mostly anything and it'll run smooth on a

1. First off, don't think too much about what programming language/framework to use. For such a user base you can use mostly anything and it'll run smooth on a low spec server. Using Ruby and Rails for a website with 5-10k users (assuming they're active users) will definitely not cause problems or empty your CC. 2. Do not invest time and/or money in learning another programming language or framework until you are sure that for a specific component of your product, programming language X will perform at least 2 times better with 2 times less HW resources. 3. Stressing again on the app stack (I saw some really pushy comments on changing the programming language), it is rarely the bottleneck of a web app. You'll scale your storage stack way earlier and more often than the app stack. 4. Know your data. That's how you decide if it's better to use a RDBMS, document store, k/v store, graph database etc. Like I said before, you're going to scale your data before any other layer becomes a problem so choosing the right data storage solution is crucial. Don't be afraid to test various storage solutions. They usually have good -> great documentation and ruby tends to be a good friend to every technology. There's a gem for everything. :) 5. Scale proportionate to your business/product growth. You will have to scale at some point. But be careful to scale proportionate to your growth. For example, if the number of users will double, get the hardware that suffices that growth. Less HW resources will lead to a slower user experience thus user dissatisfaction. More HW resources than needed will increase your costs and the resources that are not needed will stay unused. Why waste money?! These are my 2c. As your business gets bigger - I hope it does - other problems will occur. But usually these things will last up to 100k users. Disclaimer: this is for a generic web app as you didn't give us any details. Depending on the app, some of my points might be inaccurate or invalid.