Box design questions

I have two Orion XTR Series 2 subs (10"), SVC.  They're pretty old and I'm having a hard time finding manufacturer specs on them - and even if I had them, I have a couple of questions:

1) Is a sealed or ported box better?

2) I'm not sure what size box is needed, but I've found a few things on the internet that says .65 cubic feet per chamber - the current box I have is almost 2.5 cubic feet.  Is my box too big?  What problems will that cause?  What if the box is too small?

3) Is there a difference - in terms of sound or performance - in going with 1 box with both subs or with 2 boxes with 1 sub each?

If it matters, I listen to mostly metal (Korn, Slipknot, etc.) with some rap and hip-hop.  Thanks in advance for any advice.

Sorry, I forgot to include this question above:

4) Does it make a difference where I buy the box?  It seems like the ones you get at a chain store (Best Buy) or local installer are much more expensive than ones I can get at some smaller shops around me, and they all seem to be made of the same material, same thickness, carpeted. etc.  Is there any advantage to buying the more expensive boxes?

Here's some input:

1) Neither is "better."  It depends on the speaker and what you are trying to do with it.  Some speakers work better in sealed enclosures, others better in ported.

2) You need the T/S parameters of your subwofer before you will know for sure.  I suggest you send an email to Orion and ask for the spec sheet for your woofers.

3) In general, seperate chambers for each sub will give you much more controllable and predictable results.

4)  You should buy or have made whatever is the proper enclosure for your woofer.  It is impossible to say anything about the quality of the enclosures you have seen, but in my opinion working with a local small shop is always preferable to the big box stores or trying to find something on the Internet.