1) most cards will work but no guarentee etc, and from what i have seen its a mixed bag performance wise - even with onboard ide/sata iv seen some rigs limit at 0.5mb/s when the hdd's within windows will do 70mb/s sustained (network transfers) - tried all different combo's and most sucked compared to windows so.
2) RAID5 is cheap (hdd wise) but expensive (hdd wise) and hard to recover from a real bad fault, raid1 or 10 is the better option, then again use a few RocketRaid 2300's (PCIe 1x RAID5 card, not true hardware but ok performance) - just keep in mind its not a total backup solution - they still suffer from patition/data corruptions, total failure and virus's etc
3) freenas is the alternative, it sucked aswell but seemed nicer then the others, easy to setup (last time i used it - last year?).
All the free ones you mentioned i did extensive testing on them (RAID5 software tests etc) - physically removing hdd's while active etc, replacing drives - i didnt like the RND test results concidering 1/3 of the time i couldnt rebuild my RAID5 array because 1 drive was missing, or running a disk check unmounting my volumes and damaging them never to be accessed again etc - no thankyou
This was across ~5 platforms and ~10 hdd's, 3 raid cards, all different chipsets for motherboard and network - overall if you want your data safe do it PROPERLY
My end result for my new server BTW (1 year old now maybe):
E5200 (most low end power efficent intel cpu at the time)
Intel DG43NB motherboard (intel = stock standard and stable, Intel network, intel everything onboard = rock solid, low cpu overhead etc)
2x2gb kingston value series DDR2-800 (reliable as hell)
Antec 300 Case (side pannel sealed off so total dust filtering, 2xfront fans too)
Corsair VX450 PSU (high efficency, lots of sata plugs - 6 etc)
3xWD 1tb Green series hdd (power efficent etc - 2tb TOTAL RAID5)
3xWD 1.5tb Green series hdd (upgrade from original - 3tb TOTAL RAID5)
1xWD 160gb (OS HDD) + 1xLG IDE DVDRW (install drive)
2xHighpoint RocketRaid 2300 RAID5 cards (pcie1x, 3xHDD per card)
"Windows Unified Data Storage Server 2003" (yes there is such thing) - using its SiS feature - read up on that awesome feature (believe linux has a similar thing tho so dont get me wrong theres alternatives but not in free NAS os's)
Been using this baby for a year now i believe - reliability 100%, never seen an issue, iv cleaned out the front dust filter once since the only air into the case is through it so no servicing the rest of my system, it hosts media, game installs, random usage and access etc and never ever has a hickup so i can honnestly say the components i listed are good if you have the $$$ and availability.
Hope this info helps - i did alot of research into all this so if you have any questions ask away mate.