That highpoint card only does software raid--that's why it is priced so low. It will do fine for any RAID level that does not include calculating parity information (0, 1, 1+0). If you run a RAID5 with that card, it will use processor cycles to calculate parity information (read: it would be slow). So buying that card is the equivalent of slapping 8 6Gb/s SATA ports on your motherboard 1) without adding any hardware to control it 2) to take away bandwidth from your other PCIe device (I'm assuming it's a gpu).
I also found the RAID controller market very confusing. Customer reviews are less reliable, I think, because the technology is more esoteric and used for more varied purposes than a processor or more basic component.
To answer a few of your questions: you can get a hardware raid controller for $300 - $400 that controls 4 drives. A hardware RAID controller is going to have specs for its RoC (Raid on Chip) as well as cache specs (which the Highpoint card lacked because it's a software card, though Highpoint does make true hardware raid controllers--they're priced like everyone else's).
You get a BBU for a hardware RAID card because it has a cache (that acts like RAM) that it uses to write information to the array. If the power goes out and there's stuff in the cache, it's gone forever. My understanding of the BBU is that you do not need a BBU if you have a UPS. However, the UPS does not protect your data from your dog getting her leg wrapped around your computer's power cord and unplugging your computer from the UPS. The BBU will sit inside your box for 72 hours (on full charge at least) holding onto the cache data for you until you can restore power and write the cache data to your array. I just got a UPS and kicked my dog out of my study.
So I eventually just picked four equivalent cards and then looked around each manufacturer's website to compare the documentation and support services they provide. I liked the 3ware card best because it has really thorough and clear documentation.
Also, you should consider what drives you're using for RAID5. The major threat to RAID5 data security is not a dual drive failure (RAID5 can tolerate 1 drive failure, but you lose all of your data if 2 drives fail) but rather an Unrecoverable Read Error (URE) while rebuilding after a drive fails.
--the following argument is based on this really helpful article that examines the exact setup that you're considering: http://www.standalone-sysadmin.com/blog/2012/08/i-come-not-to-praise-raid-5/
If a drive fails in your RAID5 and you replace it, your controller must read the (3TB worth) parity info of the remaining drives in order to write it to the new drive. Consumer (even WD Black) drives have a URE rate of 1 in 1e14 (this is usually found on the manufacturer's website), which means that you can read a full 3TB HDD about 3 times before it is extremely likely that you will have a URE. So when rebuilding (and reading) there is a much better chance than you would like that you will have a URE and your data goes splat.
That said, enterprise drives have URE rates of 1 in 1e15 (that's almost 40 reads for a full 3TB drive). Of course these are more expensive, and some "enterprise" drives still have URE rates of 1 in 1e14--make sure you check the manufacturer's specs.
These are the low URE rate drives that I got:
http://www.newegg.com/Product/Product.aspx?Item=N82E16822149449
WD's RE4's have low URE, and so do Seagate's ES.3's
edit: here is what crystaldiskmark told me about my 5 disk raid5 setup with the 9750-8i on toshiba MG03ACA100's:
http://i.imgur.com/WOnvaxn.png