HP ProLiant N40L MicroServer, which setup?

So, following on from my previous post (Follow up on which NAS question) I now have a HP ProLiant N40L MicroServer, but I haven't actually done anything with it yet!!  I now have a ton of questions re the ProLiant.  I have scoured the interwebs and there have been some great forum posts in relation to this, but I still ask here as well.

Intended use

I had initially intended to use the ProLiant as a server, while still using my Dell as the main HTPC, however due to the random restarts I think I will use the ProLiant as my HTPC, connected to my TV.  The intention is to give the Dell to my parents, who will just hook it up to their existing monitor and use as a normal PC.

The ProLiant will also run a Logitech server and probably a server for all files and documents across the house (with appropriate backup in place) and also maybe stream to the TV in our bedroom.

Hardware setup

At present I have only taken the ProLiant out of the box (and put it back!)  I intend to go shopping over the weekend for various parts (in HK online shopping doesn't work so well and I will have to hit one of the big computer shopping malls, where ironically prices are actually often more expensive than in the UK, even though most of the parts are only made 20 odd miles away across the border in Mainland China!)

My planned set up, like many people is as follows:

- Move on HDD to ODD bay for OS
- Get more RAM
- Buy graphics card
- Buy hard drives

Moving HDD to ODD: From what I understand this is pretty straightforward.  I could either get an ICY box for 5.25 to 3.5 convertor or get some nexus brackets, a SATA data cable and molex to SATA power cable.

RAM: The onboard RAM is 2GB.  Now do I add 4GB (making it 6) or do I go for broke and add 2x4GB (making it 8GB)?  I think 6GB will be fine, but 8GB will give a bit more overhead esp if I intend to use it for several tasks at the same time.  From reading I understand I need 240pin DDR3 PC3-10600 (1333 MHz RAM).  Also it seems that it doesn't matter if I get ECC or non-ECC ram.  I think non-ECC is cheaper, so will probably opt for that.  Any other RAM I should consider?

Graphics card: From reading the forums, it seems the Radeon HD 6450 low profile card is a good choice (BTW what is the difference between things like Asus 6450, Sapphire 6450, etc?)  Or should I go for the HD 5450 card?  I'm just going to be using this graphics card to connect the ProLiant to my TV with HDMI.

Speaking of graphics card, I presume these come with sound as well, or will I need to get a sound card as well?

Another option I was thinking of was just using my AMD 4330 from my Dell.  I know its not great, but it does kind of do the job.  This does mean no graphics on the Dell, will this even work?

Hard drives:

This is two pronged - HDD for OS and HDD for storage.

- The ProLiant comes with a Seagate 250GB 7200rpm HDD and it seems quite a few people are using this for their OS in the ODD bay.  I am thinking of doing this as well.  I also have the 1TB HDD in the Dell.  I was thinking about using this as either storage or as OS.  I also have a spare 60GB SSD which I was thinking about for OS (but I guess that depends on size of OS, again to be discussed later).  If I were to use the 1TB HDD, could I partition in a way that some of it would be usable for OS only and the remainder for storage (mainly for documents and files, NOT media).

- For storage - i.e. in the four bays, which HDDs are better? WD Green or Seagate Barracuda?  They would be used for media only.  At this stage I am not sure how many HDDs I intend to buy (if any at all, for example if I use my existing 1TB HDD).

- Also RPM?  From what I have read 7,200rpm for OS and either 5,400 or 5,900 rpm for storage.  The 1TB HDD I have, I was thinking about maybe using for media storage, or would that not be such a good idea, because of power consumption reasons [I would replace the HDD in the Dell with a spare 2.5in HDD I have]?

Also, should I be hacking the BIOS?  From what I have read in the forums I should only really need to do this if I intend to use an SSD as my HDD?  Is this correct?

Operating System

I guess this is the biggest issue.  Which OS to use?

Originally the intention was that the ProLiant would just be a server, then I would have just used something like Openmediavault or WHS11.

As I now going to use the ProLiant as an HTPC, ideally I would want to use Windows 7 (sorry, mainly a Windows guy), however the cost is quite prohibitive.

From reading WHS11 has got quite a few fans as being quite a good set up and not too badly priced.  Now, would I be able to WHS11 as both an HTPC (as I would need to install front end like Plex or XBMC) and a server [all the other computers in my house are Windows based]?

Or what about Windows 8 Consumer Preview, or that a bit too risky as its still in trial mode?

Through Dreamspark I do have access to Windows Server 8 Beta and Windows Server 2008 r2, as these considerations as well?

If I were to go down the WHS11 route, it is actually not available in Hong Kong.  I don't mind buying it through Ebuyer, etc, but it seems they actually send you the physical discs.  Could I just download it from somewhere (where?), buy WHS11 and get it sent to my parents house in the UK and get them to email me the serial code?  Would that work? How big is the WHS11 install?  Would it install on my 60GB SSD, or is that too small?  What is the smallest required hard drive space?

Or any other OS that would work?

RAID set up?

Now I know this will really depend on which OS I go with, but from reading it seems RAID 5 is a good balance between redundancy and speed.  Initially, I am actually thinking about going with RAID 0 as I may only buy two HDDs (or I may just use my existing 1TB HDD).

If I go Windows based it seems I will have to use a software based RAID setup, something like FlexiRAID?  For RAID do I have to buy the same sort of HDDs (size, brand, etc), or can I mix and match?  Also, will JBOD work?  I have not read anything about using JBOD with the ProLiant in this forum, but would just want to check.

Conclusion

Firstly, many thanks for actually reading this very long post.  I do apologise for this, but just wanted to provide as much information as possible about my questions in one post.

I think initially I will only run with my existing 1TB HDD (just a cost issue) and then will expand later on.  I still need to decide whether I use the existing 250GB HDD as my OS hard drive though, or use my spare 60GB SSD.

I do appreciate any comments / help / suggestions you may offer.