Welcome to the forums mate
i commend you for wanting to having a go at being a sniper, but as someone new to airsoft i must advise against it. don't get me wrong, i don't know you, you may have a military background etc, but the physics of airsoft differ drastically from those of a conventional gun.
In the real world fire fights, distances can range from less then 100m to 2Km! yet in airsoft a fully upgraded sniper may struggle to hit 100m. Wind, rain, infact anything can blow your BB off course.
i say "upgraded" in a loose sense, as most sniper rifles will require some upgrades at some point, and if you want to max them out .... its not cheap
one thing you may be aware of is that bolt action snipers usually get a high FPS allowance, this is nice as it lets them run heavier bb's (which are more expensive) and they trend to travel further. however if you are using this higher FPS it comes with a penalty, as you will have a minimum engagement distance.
one thing most players over look is the hop, this is what allows the bb to go even further, and can govern accuracy (the barrel of the gun dose not have anywhere near as much effect on accuracy/range compared to the hop). also large FPS spring snipers have a heavy bolt pull (arm ache!) and as you increase the FPS, this adds strain/stress to trigger components that can and will fail.
let me just finish by saying that a good quality AEG can hit somewhere near 60m, an out of the box sniper may struggle.the AEG will fire a hell of a lot faster and be more reliable and versatile in the long run. and if you wish you can always switch it to semi auto
edit :- forgot to say, have a look at ian's newbie guide, its full of good info, and makes a good reference point for new and experienced players alike