I lived in the Taupo area for a few months back in 2008, and aside from the mouth of Waitahanui, and the famous pools on the Tongariro - I didn't find it particularly hard to get away from the crowds. In fact, most of the time I was happy to run into other anglers because it was fun to visit with them and a great way to get more intel on the area. The rare times that I left the Taupo area to fish I found the angling pressure to be quite light. Mind you, I was mostly fishing week-days, and was off in the South Island during the absolute peak of the December holiday season, but at least back then getting away from the crowds was rarely a problem.
In fact, the fish in my profile pic was caught on the Tongariro not all that far from some of the famous pools. I basically had a very nice stretch of the river all to myself for several hours during the late summer, and got to watch a conga-line of trout in the 5lb+ range reject every dry in my box while they gorged on a steady-stream of lacewings, until my wife said "Maybe you should try the mouse fly...."
If you want to explore on your own, getting your hands on a copy of "Volcanic Trout" by Brendon Mathews is a good place to start. That book alone provided me with way more places than I could possibly have investigated during my time there, and as I said above I almost never left the Lake Taupo zone to fish because there really wasn't much upside to doing so from a fishing perspective.
The going rate for a guide was $500-600 per day when I was there, and I had time to learn the ropes on my own so I didn't really even consider coughing up the money for a guide, but if was heading there for a short trip I'd definitely pay a guide for one day at the start of the trip to get oriented and perhaps score a bit of bonus intel and then head off on my own from there. I'm not sure if he's still around, but there was an American physician that I met while I was there that booked a few days with a Taupo-area guide named Andrew Christmas and had very good things to say about him. I also generally found the folks at the local fly shop in Taupo to be quite helpful and friendly when I stopped in to buy something, which was fairly often.
The last thing I'll say is hopefully at least part of your stay overlaps with the cicada hatch. I was there for the full cicada-cycle and all I can say is that I was sad when it was over.
