Our baby is going 6 months this week. He has his first 2 teeth at the bottom gum popping out on the 4 month. Development stages described in babycenter seem pretty accurate.

Nothing to worry about but baby will be drooling a lot as they have not learn how to swallow their saliva. The drooling will be lesser when they start eating solids at about 6 months of age. When they are served with the spoon, they will use their tongue and swallow, this is when they learn to swallow their saliva too.

I dont know, better consult a doctor