1) I just swallow at the start and my tongue becomes well connected to the roof of my mouth. If I don't then the tip stays in contact.
I don't move it. Relaxed stillness, in the correct position, is what I try for during sitting meditation.
I've had the "sweet water" in a mouth a few times. I found I spend more time thinking "do I swallow or not". It became a distraction from the meditation. So I recommend that if your consciousness has come to a mouth of saliva, then swallow and get back to the meditation.
2) Once a meditation starts I keep my tongue against the roof of my mouth until it is down. However, during a walking meditations, I often breath in through the nose and out through the mouth. Thus breaking contact every breath. (good, better, best... for now it's better to get enough air).
3)My guess is that it is just your way of experiencing qi. Stay with the meditations as best you can, in a calm and confident manner. You may find that your experience of qi will change as your develop in the practice and open your channels wider.
You are perfection.
Iam2 
