One thing you might want to think of in the beginning is the amount of space you require for applications and data. The standard version of BBB has 2 GB flash memory onboard and newer ones have 4 GB. In this book, I describe my strategy of using one additional memory card for the master node and additional external network storage for shared libraries.

A critical feature of computational nodes is the amount of RAM they have installed. On BBB, this is only 512 MB. If you are of the opinion that this is not enough for your tasks, then you can extend the RAM by installing Linux on an external SD card and create a swap partition on it. However, you have to keep in mind that the external swap space is much slower than the DDR3 memory (MB/s compared to GB/s). If the software is nicely programmed, data can always be sufficiently distributed on the nodes, and each node does not need much RAM. However, with more complicated libraries and tasks, you might want to upgrade some day...