Whats the best filesystem for the MicroSD in my omega 2+? ext4? FAT32?
If your usage is linux only, I'd suggest ext4, however for portability across systems, stick with fat32.
Whats the command to format the sd card from the command line?
For ext4, first identify the device name and current mount point of the sd card, then:umount /dev/YOURDEVICE mkfs.ext4 /dev/YOURDEVICE mount /dev/YOURDEVICE /PREVIOUSMOUNTPOINT
You may have to install some packages to get the mkfs tools. Refer to What is OPKG? for that.
For fat32, I'd suggest you locate a tool called 'SD Card Formatter'. It's a windows gui tool, perhaps there are linux ports, I'm not certain.