Just to query it some of those devices will do fine but DNLA is a joke in my experience so you may or may not want a device that transcodes on the fly. PC and android will probably do fine with most things but the PS3 and Wii U may struggle a bit (pending hacks of each mind you), stuff like TVersity has existed for years to cater to this segment though. On the other hand if you already have media encoded in a form it can happily play with I will shut up.
Keep in mind that RAID is not for backup and never will be. You still need to make another backup, be it external hard drive or BD-R. Just because RAID 1 is mirroring does not mean the data is safe from corruption. It is actually the opposite, when a data differs among drives RAID has no idea which file is the correct one.
Absolutely +1 that RAID is not backup (it is pretty much the zeroth law of data backup) but I have seen some of the more fun levels of RAID on consumer level NASes, if you are doing something like freenas then all bets are off.
For the most part though I will echo the others in that you want something like a NAS. The four options seem to be
Basic piece of junk, for not an awful lot you can get a small case which holds a few hard drives and runs a very cut down, almost locked down, version of linux at its core (probably only a web server and maybe SSH to access it) and will probably do a basic line in SMB (standard windows shares, also samba on linux), FTP and maybe a bit of upnp and other such protocols. May choke on the many streams thing.
Small device build. Historically this was stuff like the pogoplug but you have a few more options now and this probably means most will look at something like the raspberry pi. They make fine decoders but not really for heavy use streaming things.
Proper consumer/low end professional device (
http://www.theregister.co.uk/2013/04/25/review_wd_sentinel_dx4000/ ). These cost quite a bit (that one linked seems somewhere slightly north of £600) but will run a full version of linux or maybe some version of windows at their heart and do the job really well.
Freenas, openmediavault..... Got an old PC sitting around? Slap in a UPS, maybe a raid card and obviously a selection of hard drives and you have something at or above the level of the other things mentioned for a fraction of the price. My experience of those operating systems is good, probably something like "treats its friends well and is not all that fussy about the ones it picks to be its friends". I would be wary to say straight windows is a good idea but for media and the like it does do better than a lot of the linux options, though they do have mythTV there which is something else worth considering (do you want this to record TV?).
Once each of those is set up it (easily done if you have ever done things like shared folders over networks) it is pretty easy to work it all, add new stuff, manage the drive and more. You might still get called in to manage it but the simple playback bit happens easily enough.
Also for what it is worth many routers will have a USB slot on these days, a 128 gig USB drive can go quite a long way if you want it to and will give you an idea of how much of a pain it will be to set up each of those devices without breaking the bank.
