The best quick read on Ethernet that will give you some background is at
WIKI.
Currently, gigabit (1000Mbps) Ethernet is the most common found on new devices and is as you would guess 10X faster than the old Fast Ethernet (100Mbps). As long as your router and device Ethernet adapter support gigabit you will be able to transfer files between such connected devices at around 120MB/s roughly (there is some overhead) assuming that your storage devices can accommodate those speeds.
RAID is an array of disks that allow for redundancy and/or faster speed depending on the type used. Again, the best quick read to get an appreciation for RAID is at
WIKI. The most commonly used redundant levels are 1 and 5 -- 1 just has a second disk with identical information written as on the first, while 5 allow use of many more disks and writes only some information on each disk with the ability to sustain the loss of a disk without losing your data.
I do not recommend using a motherboard controller for RAID though, as any bios hiccup can break the array.