You are correct, you must use a poweramp, whether the poweramp is external or built into the speaker cab. The POD cannot drive a speaker cab on its own.

I've been thinking of getting one of these, they've been on clearance for a while now. http://www.americanmusical.com/Item--i-ALE-RA500-LIST

The problem you'll have is that solid-state amps like either 4 or 8 ohms and your 4x12 cab might be 16 ohms, it will work but you won't get all the power that the amp is capable of making. If your cab is 16 ohms it is really easy to rewire it to 4 ohms which is perfect for a solid-state amp. I use both so I put a toggle switch in mine to select 4 or 16.

Either one of those would work. Depending on how loud you want to get, I would try to get at least 100 watts if you are playing in a band, for practice that 22 watt would probably do pretty nice. The thing to remember is it takes about 2-3 times more watts in a solid-state amp to equal a tube amp.