Cabinets...

Well with heavy particle board the weight difference is not necessarily marginal. 
 
And keep in mind that you don't want a closed back cab without a speaker in every position, or it isn't going to work like a closed back anymore. 
 
As it happens, this was my Christmas present to myself this year (I know I know... ):
 

 
It's a 1x15" convertible back guitar cab that I put an Eminence Legend 1518 speaker in. I got the unfinished cab from this guy:
 
http://www.trmguitarcabs.com/index.html
 
or on ebay:
 
http://www.ebay.com/sch/wolfgang2204/m.html
 
It turned out that buying a nice 1x15" cab from there and having to finish it myself and choose and apply the grill cloth, piping, handle and feet didn't cost enough more than a cheap new cloth or tolex covered cab to make the savings worthwhile. Of course it took a bit of work and the grill cloth isn't just exactly perfect, but aesthetically it's much nicer for my purposes (I like wood ) and it doesn't leave the house so I don't need any better protection. YMMV.
 
But for a ?x12" cab, there are many more options available than a 1x15" (guitar) cab and you might find something very cheap, or you can just pick up a broken combo somewhere cheap and convert it to a cab.
 
Of course you could also build one yourself, or maybe you know someone who can build you something simple. Most guitar cabs aren't ported and are basically just a box big enough to put the speakers in with either an open or closed back.

Hi Rain,
 
In my opinion, the cool thing about buying an already made cab is....the wood is supposed to compliment the speakers inside it. I've always liked Marshall slant (tops) cabs because they don't "woomf" with low end. My weapon of choice is the 25 watt greenback Celestion. I like them because:
 
1. they don't need loads of gain to break up...they do that on their own nicely
 
2. They are one of the warmest speakers I've ever played through
 
3. They have one of the most focused sounds for recording of all time (meaning, they are made for close mic'ing yet still sound pretty good up to 6 ft away. After 6 ft away though, they start to lose focus because they are made for close range. Whether or not a cab sounds good after 6ft usually means it sounds bad up close or is pretty bassy. from 0-4ft is what matters to me. All the rest comes through the mic really.)
 
4. They don't have to be loud to sound good.
 
I like them over the regular 75's and the vintage 30's you talked about because the 25 watt greenies don't have that harsh back-tone. The 30's have a sizzle that I just can't stomach and just don't sound as warm, and the regular 75's (the 300 watt cabs) have a 5-6 k nasal sound that is just not for me.
 
I've tried these speakers in my own enclosures as well as some others have built and unfortunately, they just didn't sound good. They only seem to sound good in the Marshall or Mesa boxes. If I were you, I'd definitely invest in one good cab with the speakers you want in it.
 
My old guitar teacher got these little Marshall mini cabs a few years back. They are like 1/4 the size of the ones I have but are still loaded with 25 watt greenbacks. They sounded awesome....and one of those would probably be perfect for you for recording. You'd have the big cab sound with a smaller space taker. I don't know what the heck those things are called, but they were amazing and sounded just as good as mine at about 1/4 the size.
 
To me, nothing sounds like a 4x12 cab especially for rock. I've used 1x12, 2x12, they all sound good....but man, 4x12 just gives you a nice pallet to work from. 2 57's on a 45 or 90 degree angle on the top and bottom, a 421 where it sounds the best to your ears and another mic of your choice getting the room and whew....you get quite a wall of sound at any volume. Check out the greenbacks if you haven't. In my opinion, they are the best Celestion I've ever used and they can be used for everything. Good luck!
 
-Danny