Well the whole reason we suggest you be a rifleman before a sniper is primarily to get used to the physics of airsoft.
Your a hunter, that's great, you've got the stalking down to a tee.
Now you have to get used to a whole new rifle, new distances, new compensations.
Since you have lots of experience shooting, there's no reason for you NOT to buy a sniper rifle. It's just a good idea to get an AEG to try it out, worst case; if you don't like airsoft, AEG's are easier to sell!
First off, your going to want a name brand sniper rifle. The tokyo marui VSR-10 is widely regarded as a really amazing platform. And the peak performance of your rifle is only as good as the base you build it from.
So just for starters, 380fps spring, hopup rubber, 6.03mm barrel. That will give you REALLY great range and accuracy right off the bat. At 380fps (on .20s) you should be using .28g BB's, as they will give you the best range and accuracy at that velocity.
Later, you can buy a PDI cylinder set (~$250) and upgrade to 440fps on .20s. Then you can use .30g BBs for optimum range and accuracy.
There's not much of a point going past 440, I've found above 440 your accuracy actually decreases unless you use the significantly more expensive .36g BBs
As for barrels, the bore means dick. a 6.01 will shoot just as accurately as a good 6.08, but you have to clean it way more often.
The big thing with barrels is the consistency of the bore, and that pretty well goes entirely by name brand. So laylax or PDI would be your best bet!
tighter bore = slightly higher velocity
I myself use a laylax 6.03, 430mm length. I get the same range and accuracy of a 6.01x650mm PDI barrel.
And as for differences in paintball, it really depends who you play with and where.... Everyone has a different style of game and different field
It's a different role on every field. In the summer at our main field I'll have a typical engagement distance of about 40 feet, the winter closer to 100
On our old field that we lost, I'd be engaging anywhere from 15 to 220 feet (people WILL get that close if they can't see hear or smell you!)
Overall I would say it's a more boring and challenging role than being a rifleman, but every kill you get is MUCH more satisfying!