I will address you points in order.
1. You can fairly easily achieve 150/165/150 stats. With a +50 stat cap scroll, you just need 115 stats from gear, which is not to hard to achieve. I would prioritize Str in all builds, Int in most builds, and Dex if you want to use healing, which there is no reason not to use. You can have permanent bandage coverage with UOSteam/Razor/EasyUO. I prefer EasyUO for my bandages so i can still do things with Razor. Lastly, 150 Str gives you 300hp without any hp increase on your items. (26 hp increase has the hidden effect of boosting you to 300hp as well). This would likely be the ffirst major survival power up you will hit. It makes all the difference.
2.Black staffs are cool. I would still recommend a double axe though. It seems you wish to go down the Macing path, which you can still do by deeding Use Best Weapon on to an axe. Two major benifits of this are that Lumberjacking gives axes a damage boost and most weapons produced by players are axes or bows, so the availability is good. And with incidental amounts of Swing speed increase it will still swing at 1.25sec. In the case of the double axe, it has whirlwind and double strike, which can be really good in single target situations (hit spells can trigger of both strikes). Weapons can also be give mage weapon, I know for a fact from weapon levels, but I seem to remember you can also get it from a deed or from staff purchases. Not dead sure on those last two so maybe some research is needed.
3. I am not an archer, but I believe the style of bow is chosen based on your goals and the weapon abilities. It seems that hit spells, hit lower defense, and Hit leeches are what is sought after. Also don't bother with hit harm, it is based on how close you are to the target. Spell Channeling(same for melee weapons), Velocity and Balanced can be added to the bow with deeds bought for ED.
4. I am pretty sure Mage Weapon is a no go for necromancy. Necromancy is receiving some love lately, so stay tuned. The situation may change soon.
5. I do not know. I have only seen one or two people use magery/necro exclusively in PvM, and they were newish. I think melee or tamer is the way to go in PvM. (I like bard alot, lots of niche uses) Also consider making a druid caster, its based of animal taming and lore, and can be damn good in AOE situations, among others.
6. Well, its not "to hard" to find some one to trade with, so I would probably go for Magery as its worth a good bit more then the Necro one. That is a long term project though, potentially a year before it would be complete. So I don't thing this is something you should worry about.
I hope this helps, please feel free to ask follow up questions
5.