Cost! :| if you aren't up to learning how to clean a carburetor, you should only buy fuel injected motorcycles. Carburetor cleaning is required way too frequently with the crap they pass off as being gasoline now-a-days, it's practically an annual maintenance service requirement for people living in seasonal weather areas, you might even need to do it more then once get it right. imho your best carburetor parts are the ones that came original, clean them really good and see if it will run with the original parts before running out and purchasing any replacement stuff.
The part about it being stored in the cold for 3 years is a problem; everything inside there has been subjected to condensation. Condensation is water and water promotes rust. Start by draining the fork oil into a clear glass container, see how much water comes out, the water will settle to the bottom. Do the same with the engine oil, if the oil is stirred up any water in there will not be separated from the oil but dispersed oil will impart a cream colour, kinda like coffee with milk in it. Hold your glass of oil up to sunlight and see if it sparkles, like little tiny bits of metal in there :/ that is a bad thing and indicates advanced wear of metal parts. Expect to need fork slide bushings in addition to the seals, there are usually 2 bushings per leg, one top and one bottom, in decent quality forks. The bushings are teflon coated and the teflon is often worn off if the oil hasn't been changed very frequently. If the fork bushings are worn even a little, you will never be able to keep seals in it. Avoid the temptation to go with heavy fork oil, start with 10 weight, light fork oil will make for lively suspension action, heavy fork oil makes for lazy suspension :| unless you really want lazy front forks.
Any iron/steel parts inside your engine or forks or transmission or steering head bearings etc that have seen water and not oil will potentially have some rust on them. I have no idea if your barrels are steel sleeved or nikasil coated aluminum bore, it would help to find that out. Your piston rings and wrist pins etc are definitely steel, but fortunately they are usually made from alloyed steel and might not be too adversely affected. Here's a tip for you; Shell Rotella T oil the dino type Not the synthetic version, use that for your first oil change, that will clean out a lot of places that you probably don't want to dismantle to service.
Replace your wheel bearings, they are cheap and usually easy available at any decent local bearing supply. No way they don't have some rust in them now. Inspect your swingarm bushings or bearings, grease or replace or even upgrade as appropriate.
Once you get the thing running with your clean carbs, you might need to balance the carbs, that is a little tricky as you need to buy or build some apparatus to do that. Carburetor balancing and valve adjustment might be something worth seeking some professional help.
Oil everything, even use oil as your cleaning fluid! It's like cleaning a gun. Everything needs to be spotless clean and well oiled or it will jam or even blow up in your face.
... hope this helps some.
