Backplane is 4-lane 8087 connectors, cables were included. there are mini SAS to 8087 adaptors available, but personally I would just upgrade my HBA to a sas3 one, ot only to eliminate the extra cables, but also bring your speed up yo 12gb/s allowing you more futureproofing upgrades to sas3 12gb/s drives in the future.
You don't need breakout cables, the backplanes handle all of that, it can hadle sas or sata drives, or a mixture of them
There are sas3 inputs and outputs on the backplanes, so you can daisy chain them if desired., I run one HBA to front, and one 8 port HBA to back, but you could use one HBA to run all the bays if desired. (It was how it was wired this way by default)
Low profile cooler and expantion cards are needed as the motherboard cavity is only low profile (Since the lower chassis onter it is used for 12 more drive bays)
As far as bandwith, realistically the only bottleneck have to worry about is during parity checks and rebuilds.