Sorry mate, only just saw your post.
I'll start with your question about turning the crank a couple of times - Yes you should turn it twice and you should notice as you do it that the tensioner will move slightly as your turning it. Make sure the tensioner bolt is loose enough to allow the tenionser to move freely under the force of the belt. After the 2nd turn to tdc you should see that the tensioner has moved as far towards the idler as it will on it's own - this is where you should tighten it.
If it's making a noise after that i'd ask -
How old is the belt? Have you changed the idler? Have you changed the tensioner and/or tensioner spring (this is one most people don't do).
As for your plugs....well it's up to you - it won't alter any belt noises that's for sure. Just change em if they're old and worn, otherwise don't bother unless you really have your heart set on a new set.