I planted 2 Nectarines last fall they are just starting to leaf out, and have a few blooms on them getting ready to open. Most Nectarines are self fertile, meaning they will pollinate themselves, however some do require a 2nd tree of a different type of Nectarine to set fruit- or at least set a better crop. Nectarines are peaches without the fuzz. You grow them the same as Peaches. Fruit bears on limbs that are one year old (the following year after growing)- so pruning is a must as with peaches. You want to prune a nectarine to an open center/vase type, meaning that you prune out the braches that grow towards the center of the tree. This will allow maximum sunlight penetration and will set bigger, sweeter, and better fruit. You need to prune out old woody limbs once the tree grows its structural/supporting limbs as those do not bear fruit. Plant in Full sun- not partial shade areas! For sprays your first is Dormant oil spray (for any fruit trees for that matter!) You use this in late winter while the tree is dormant- before the tree buds out. Do not use dormant oil spray after the tree leaves out- it will damage foliage, and fruit. For other sprays I use Bonide fruit tree spray which is both a pesticide, and fungicide which will reduce diseases. There is a spray schedule, as well as mix ratios on the bottle- it differs from some of the other fruit trees, but just follow it. A good practice is to pick up any fallen fruit and get rid of it (this goes for ANY fruit tree) as it usally harbors insect/pest larvae, and leaving the fruit on the ground will restart the life cycle of pests. In the fall rake up all fallen leaves and get rid of it- do not mulch with it as it can restart life cycles of diseases the following year! Some people even get rid of the mulch around the tree in fall, and lay down new mulch!
I planted a Mericrest, which is supposed to be a very cold hardy Nectarine- its stated as the most hardiest of Nectarines, and is supposed to bear early in its life. The other cultivar is called Flavortop, it requires a 2nd type tree for better fruit set.

Its really the same(diseases) no matter how much, just will be more to take care of if there is more trees. Nectarines are suseptible to brown rot, oriental fruit moths, and Japanease beetle love to eat peach/nectarine leaves. Some cultivars are resistent to some diseases. If you plant more than one, there is a better chance for fruit set even for self pollinating kinds, if the trees bloom at the same time. Spaying trees isnt all that bad, just buy a couple pump up spray bottle, and use your mix in there-just be sure to label your sprayers. I use the one gallon size, made by Ortho, it is easy to carry to the trees- the cost about 9 bucks each at Walmart. Ive heard some negatives about Dwarf peaches and nectarines, something about them being less cold hardy. You can buy a standard size and keep them pruned- as they need alot of pruning anyways . A good book to look into is a book called Backyard Fruits & Berries by Miranda Smith. Its worth looking into. The books covers everything from planting, pruning, to grafting to training, and even has recipes to make Organic Sprays if you prefer organic. The photos, and illustations are great. The book is availble from Amazon, and Borders books, I bought mine used on EBay for fraction of the price. The book looks like this:

As of now I have 33 fruit trees in my home orchard, alot of them are young trees.

I started my orchard last spring, but have had fruit trees when we were kids at home, the trees were always loaded, but squirrels ended up getting fruit there. I bought a few larger trees at a Nursery not too far from me. I did alot of research into it before I started. Everything seems to be growing well so far, had a copule trees that fruited last year- hopefully this year will be better, but too early to tell. Worse comes to worse, you can always cut the tree down it its a problem.