Hi, navigator!
1) These words technically don't have much of a difference but in actual usage the tendency (note this is only a tendency, not a rule) is to use shudder to denote a negative experience while quiver is more of a positive experience, ie "The ugliness of the thing made me shudder," compared to, "the expectation left me quivering." Like I said, this is not a hard and fast rule
2) A chuckle is a pleasant sort of deep throated laugh, to cluck is to make a noise like a chicken, not a flattering way to describe someones laugh!
3) Nothing, they are entirely synonymous.
4) Once again, no difference, they are synonymous.
5) Well I'm not a smoker so I can't give you a technical description or account of comparitive taste (

) but a cigar is generally large and brown (and the best ones are said to be made in Cuba) where a cigarette is small and usually white (there is some room for differentiation in colour though, I've even seen pink and purple ones!)
6) "You may decide
by youself" implies that the one deciding will actually be physically alone when they make their decision. "You may decide
for yoursel" would simply mean that the decision must be made without aid from others.
Hope that helped!