Before starting anything I would upgrade the firmware to v1.5 and download the latest drivers for your OS as firmware below v1.2 were really bugged.
On the 2720sgl you have 3 modes that can be seen in the web interface in order to initialize the drives, it is also the first thing that you have to do in order to see your drives later:
If you choose the first two, you have to wait until the init is done in order to creat a partition and it can take hours/days depending on the size of your drives.
If you choose quick init, it does it in a matter of seconds and you can then create your array then partition and start putting data almost right away.
Think about doing a quick format vs a full format on a hard drive, same thing here.
The block size will always be 64K (strip), the sector varies from 512b to 4096b however best is to use 512b (hence the warning you got when selected 4Kb). Why? Well, drives are now using advanced format which is 4k and is necessary in order to see the entire drive space so you don't have to take care of that. See this article
on the Seagate web site for more information.
Nonetheless, the 2720sgl is a great card. I have two of them and for the price they are very fast and feature rich.