The Ninja will only heat up to 60 in the tank. Anything hotter than that might ruin the pump head.
I was also pretty nervous, but if you are only getting medium results, try buying a steammate, and if that doesn't do it, get a powerbrush. The steammate is fantastic for getting the carpet looking good. With the above kit, you can clean normal domestic carpets without any chemicals, just hot water. If the carpet has traffic lanes, a bit of microsplitters as a prespotter is plenty - it will save you lugging all those chemicals around with you.
Test your carpet types at the beginning, but when you are confident with your method, you can leave that as well. If you clean correctly, you won't damage any carpet (not including sisal etc)
I am cleaning a library next week (east london) and you can come along if you like.