Come on boyz, this is an NSR we're talking about here, not a potter down to the shops chicken chaser.
Keep these things in good working order and they'll repay you with an exhilarating riding experience, but if you don't give them the love they deserve then they'll take it out on you and try to do you damage!
The fork seals are not a big job, but you do need some special tools. Taking the seals out is easy, but refitting them without damage requires a special seal driver. But if you'd rather not deal with it then the best advice is probably to take it to a reputable MX shop as those boyz are always pulling things apart and a set of NSR fork seals will be a breeze.
Fork oil quantity depends on the model. I think Andy's got a oil level and quantity guide here somewhere on his site.