The best way, is to record your guitar track 2, (or 3) different times, (played exactly the same way). When you copy a track, it's too perfect - BUT - a trick I use if I'm in a big hurry is to copy a raw guitar track and then either move it physically, so it's a split second behind the first track, or put delay on it. If you opt for delay it's important for the delay to be at 100%. No mixing. So ALL you hear is the delayed track. You'll have to mess with the delay time to find the sweet spot. (but it's usually just a few milliseconds. It doesn't take much).Again, when the first track is panned left and the delayed track is panned right, it's easy to hear when it's "right". It just sounds huge.
So to actually answer your question - it's totally scalable. 3 amps per side. I would probably go with the same 3 amps. So amp 1 - left & right, then amp 2, left and right, etc. And I would play all 6 tracks individually - no copying.
Not sure I would go with 6 different amps. That's a lot of conflicting frequencies. Might end up being super mushy. More is not necessarily better.
Each track needs to have a purpose. Maybe one amp is fully saturated and heavy in the mids, the second amp is dirty with a lot of low end, and the third amp clean to add definition and highs. Or better still, an acoustic guitar. You'd be amazed at how many great rock tracks have a tiny bit of acoustic mixed in with the heavy guitars to add dimension and definition.
When you think big, don't just consider numbers (amount of amps), think about covering the frequency spectrum. Maybe turn down the mids on one guitar and boost the mids on the second guitar, etc. You can do A LOT of damage (in a good way) with very few tracks. Also consider different amounts of gain. Heavy saturation mixed with clean makes a guitar sound 3-D. So there is depth. Not just left and right, but near and far as well.
Another mistake a lot of guitar players make is saturation. If you listen to isolated guitar tracks from your favorite songs - they're never as saturated as you think. A little dirt goes a long way.
Hope that helps!