6x120 necro mage is the standard, it should work fine I still have several. The only downside is the mage weapon so expect disarm spams.. but you can bloodoath so you should be ok.
As for stats.. that's differnt for each person, I personally go high str for more hit points, and then I run 10 dex w/ a crimson. I don't worry about dex/stamina because of red potions and the wolf summon in a pinch. This varies for each person. So my usual breakdown for stats is 125/10/120. I don't usually carry the str potions on a necro mage.. not sure why but thats how i do it.
As for 1 v 1 that will depend on you personal skill. The hardest fight will be against a mystic in protection, but they changed apples and how curses are removed so it may work out. Mysticism was basically created to nerf necromancy however, and if the guy goes into stone form half of your curses will be resisted. Bloodoath is a standard, people complain about it but it works so use it. I suggest hitting a bloodoath early, most people will apple out of it then hit it again and debuff then blow em up. Explode, Flamestrike, Evil Omen, Pain Spike is the basic combo, I like fireball/magic arrow spam with a strangle against mages. It all varies each fight is differnt and like I said it will depend on your skill and the skill of your opponent.
Pros of a necro are the curses, you force apples, you stack lots of debuffs and you have the potential for large damage combos. Also necro mages kill sampires pretty well. Necros also can throw a rev on a stealther and keep them from hiding. There was a bug that revs got dispelled in guard zone.. not sure if this still exists or not. Strangle is awesome, and EO + poison is almost never resisted. A lot of poison necro mages showed up recently because of this and the ability to do level 5 (lethal) poison threw magery. Mind rot is nice if you know your opponent has limited mana, as in a scribe mystic mage, running 40 med and 120 focus is ok but if you can chunk the mana out faster it hurts, it also makes dexxer specials cost more. Spiritspeak is also very strong, it's the best way to heal threw mortal wound and you can get free heals from dead bodies. EO is the best spell in the game I think.. use it a lot, 120 resist=60 with a quick little spell. And well.. wither.. if you don't know about wither then play a crafter..lol
The biggest con is the mage weapon, you WILL be disarmed.. a lot. Bloodoath helps to counter this but it's not a sure thing and if you get more then 1 person on you bloodoath won't do much. Fencer/archer and ninja dexxers love mages who use mage weapons. If I fight a constant disarm spammer I will go into protection because you really can't do much else. Also deathstrike damage is bloodoath..able.. so I have often taken a deathstrike, bloodoathed and ran to kill the guy. I take 60 but he takes 50 and follow with a 30 dmg pain spike I like the trade off. Have to be carful tho, bloodoath is a risky spell sometimes. Necro mages are also mana hogs.. they use lots of mana and if you arn't carful you could spend a lot of mana debuffing to have the guy apple out of it and then have to debuff all over again. Bloodoath usually forces an apple, and curse is greater then corpse skin 9 out of 10 times. I can't think of much I don't like about necro mages aside from the mage weapon. They are the best all around character I think, pvm great and pvp great. Great for chokes and great open field.. I like them a lot. The hardest thing is they are not easy to play, compared to a mystic mage the necro seems extremely complex. Oh also I find that without potions necro mages can be hard to play.. but I use bloodoath a lot and so I chug heals to counter the extra damage I take. The cure and refresh pots are important but the heals are how I stay alive. I often will be almost redlined when I kill someone and without that heal potion I would've died. Example of hte 60 dmg deathstrike I take while I have bloodoathed the guy. I chug a potion and I gain approx. 30 hit points back. I lost 30 hit points then vs him loosing 80.. assuming he chugs a pot he looses 50 .. still works in you favor, his heal pot only canceled out your pain spike, while your heal pot cut his deathstrike in half. This obviously isn't concrete but it's an example of how heal potions can make bloodoath extremely effective.
I think I rambled enough ..lol good luck with it and just try to adapt to each situation best you can.