it should be more widely known that babies NEED to suck. and the kind of sucking does matter... and different kinds of sucking helps strengthen the muscles in the face and actually contribute to how the child smiles!
if you are nursing, try to nurse at these times. he might actually be hungry. it may seem that its often, but what you want to do, nursing or bottle feeding, is to nurture the need, so that it doesnt show up as an undesireable habit later. i know a child who wasnt allowed a nuk didnt start sucking his thumb, but grinds his teeth! drives me nuts LOL.
its good that he takes a nuk. the problem at this age is that if he loses it he cant really get it back yet, just keep offering the nuk, and give it back when you can.
with a sucker i wouldnt think the thumb is going to be a permenant thing.
as far as left hand right hand, its WAY too early to start thinking about that. and it doesnt matter one way or the other. your child will write with whichever hand works best for him, and it doesnt matter which one that is. dont encourage him to use one or the other, but dont stop him from using the one he chooses either.
good luck, and keep up the good mothering!