When making back up images of my machines, I also use my NAS to store those images. I only have a 10/100 connection for my home LAN but have found it adequate for direct writing of the image file from the machine being imaged to the NAS. I am also averaging 82Mbps LAN speeds across my 10/100. Gigabit LAN would/should be faster but a lot also depends on the NICs, the CAT5 cable, hard drive speed, and the router being used.
When it comes to direct writing across the LAN and/or to a CD/DVD disk, I have observed that it largely depends on the software being used to create the back up image. Some imaging apps are crap when direct writing while other are pretty snappy and have no issues. Currently I am using
Macrium to create my back up images and it has been working pretty well for me.
As far as PCIe RAID controller cards, opinions will vary as to which one is the "best", but I have been using 3Ware cards for years and have found them to be very reliable. For an 8-port SATA card, I recommend the
3Ware 9560SE-8LPML ($490+/- new/retail) or the
Areca ARC-1220 ($440+/- new/retail). They are expensive cards but, IMO, worth every dollar. Given the price, an option to save some cash is to peruse eBay for used controllers. I've snagged some used warez at very reasonable prices over the years off eBay. Also check out Highpoint and Promise controller cards; but the important thing to remember when selecting a controller card is to be sure that it has an on-board I/O processor, otherwise it is not truly a hardware RAID controller. No on-board I/O processor = fake RAID!
Regarding guides to set up a RAID array using a controller, the manual is a good place to start. You can DL the manual from the makers support site and read through it before making your purchase. But mostly, it is a pretty straight forward process once you get past the jitters and jargon. Fact is, setting up a brand new RAID array using a hardware card is almost fool-proof given that there is no data on the array to lose; so, you can configure/delete and configure/delete until you are comfortable with all the controller options. Also, most/all hardware controllers have a web GUI to help with configuration if using the controller BIOS makes you nervous. Personally, I prefer to use the BIOS to configure the controller, but that's me.
Lastly, building a purpose built NAS solution using either FreeNAS or Openfiler, even with the cost of a hardware controller card, would meet your data needs and stay within your budget.