Beyond that, capacity requirements depend on two things: the length of time your page requests take (say N seconds), and the number of simultaneous surfers you want to support during that window of time (say M surfers).
You need a Hub that has capacity M to support M people during the N second window. Here's why... let's say a surfer comes along and runs a query at your site. Let's say that query takes 5 seconds to run. If someone else comes along during that time, they will have to wait in line -- unless -- you have another instance of your EXE available for that second person to use.
We generally recommend the 5-exe Hub, which gives you the ability to run 5 instances of your custom EXE and therefore serve 5 simultaneous surfers during your N second window. Sites with longer query processing, or with more than one web application being deployed, or with very high traffic requirements, will obviously need more than a 5-exe Hub. You can obtain an unlock code for your Hub, giving it a higher capacity, at any time. Unlocking your hub is a simple (1 minute) procedure which does not require reinstallation or recompilation.
What is a "deployment machine?"
It is the machine that you run the final system on. Most developers have one or more development machines that they use to write systems on, and then they "deploy" their software on one or more machines for use by other people.
What should I install on the Deployment Machine?
How is this different from my Development Machine?
Your development machine will have all the items above, plus your development environment -- Delphi and all the source code to your EXE.