Shelves can be hot added with no downtime. If you have never added shelves, I recommend getting an hour of professional services and the PSE can show you how they connect both the SAS and ACP connections and confirm everything is working with multiple paths on both. Then disk assignment and aggr grow or create.
There are shelf configuration guides that give cabling diagrams and commands in detail on the now site that you should read if you are going to do it yourself. The guides are very good and give examples.
You might have a install support included, there used to be a number along with the delivery where you can call and schedule a onsite install.
If not ceretain please ping the NetApp sales rep assisted on this purchase.
Do you have existing SAS shelves in your environment?
DS4243 can not be mixed with a stack containing DS2246
Also please ensure the shelf ID is correctly set if you are hot adding to a existing SAS stack, if not there will be shelf ID conflict and you might end up needing reboot of affected shelf to clear.
There can be maximum of 10 SAS shelves per stack.
Ensure you have the latest version of IOM FW installed (sysconfig -a will display compare it with what available for download on now site).As a best practice please keep this up-to-date with future shlef FW releases.