Citect SCADA License

1 client license (control or view-only). This could be located on the client PC or a floating license on the I/O server or alarm/trend server PC's key
1 full license for the I/O server PC
1 full license for the alarm server/trend server PC
1 historian license

For the development PC, it is possible to develop without a license, and run in 15-minute demo mode (with under 50,000 points) if you want to run it as a stand-alone server when testing. Or, you could get a client license and it would connect to the production I/O, alarm, and trend servers when testing--which is good for testing graphics changes but not much help for testing I/O changes. The other option is to get a full license for the development PC so it can run as a stand-alone server for full testing of the project for any amount of time. Talk to your sales person...you may be able to get a loaner key or another option that would be cheaper than paying full price for a full server license for the development PC.

On the development PC, do a full installation. I normally do full installations on the servers also, so that you can do debugging and local project changes if necessary (such as if your development PC fails). You could do server-only installations on the servers if you are strict about making all project changes on the development PC and deploying them to the servers. On the client PC you can do a runtime-only client installation. I assume you will be using the Project Deployment feature to push projects from the development PC to the clients and servers. The same setup would also work if you were using the older Copy parameter to transfer projects to each PC.