I know a wiki is being worked on to aggregate this information however here is some simple answers to your questions.
The Raspberry Pi is the logic for the OpenSprinkler Pi. The OpenSprinkler Pi has no logic or network interface and therefor you don’t need to worry about it at all after attaching it to your Raspberry Pi correctly.
The Raspberry Pi needs several things to properly control your sprinkler system. It needs an operating system which it sounds like you have (eg. Raspbian). It then needs the interval program installed available here: https://github.com/rayshobby/opensprinkler/tree/master/OpenSprinkler%20Pi/software/demos/interval_program
Honestly, thats it. You don’t even need a HTTP server for just that and you also don’t need to worry about the firmware versions. The interval application says it uses 1.8.2 but that is because it is based on the OpenSprinkler 1.8.2 firmware. The only major difference between 1.8.2 and the newer ones (1.8.3 and 2.0.0) is the sequential option which Dan is working to add back in.
I think the confusion arises when you read posts related to my mobile web app which does require a web server and requires a different port (same IP is no problem). If that is something you need assistance with I would be glad to help however I suggest getting a working interval program first then proceeding from there.