A fishy. Full skellywarriors, full skellymastery, one dot in the rest of the summon skills. I will likely go for full corpse explosion, too. I am raising it at the same time as golem mastery (I figure that golem mastery is an useful skill: it boosts survivavility of expensive iron golems, it reduces the times you have to recast clays when facing bosses, and it increases the hit chances of both). I also have one dot in all the curses barring blindness, confuse, and attract (I find little use for confuse and attract. Blindness I am considering, but I have other priorities for points). Revives is one dot, because with the +skills, the golem, and the skeleton warriors, I have a big enough army.
The thing is that many people recommend maxblock, and I am half tempted to go that way, and keep an area-of-effect crossbow as an alternate weapon (for fun, mostly). But I reckon that block is not very useful, because most of the attacks that would normally concern me are not stoppable (novas in particular), and as for arrows... normally I will be standing behind my troops. I expect them to act as a meatshield. Heck, meatshields are 50% of the point of playing a necro. Thus, I expect that higher vit to protect me from novas and stray bullets would be more useful in the long run.
Considering you must be a summonmancer, or at least a hybridmancer, your summons do the fightin, so invest your points into vitality since that build isn't meant for melee. if you want to max your block then go ahead, but i would recommend against it.
be sure to put a few points into bone spear or spirit so you can properly support your skellys.
you should also be careful when selecting the golem as well, blood golems can be handy depending on builds, but if they die you can lose alot of health. Iron golems require you sacrifice a good weapon to have a good one. i stick with fire and clay, Fire for its high health and aura, but clay for it's extreme health, and slowdown. it's best to select one, or at most two at the start.
a level 20 corpse explosin can be devastating, my necros CE is only 5 and it is an incredibly valuable, and powerful skill, even if you use 3 or 4 corpses. revives are useful on high difficulties, and when multiple people are playing.
1 Player: 120% Monster HP
2 Player: 220% Monster HP
3 Player: 320% monster HP, etc
and some can be extremely powerful on nightmare, like moon lords, in A5
The regular skill layout for an SM is
20 Skelly mastery
20 skelly summon
20 golem mastery
20 in choosen golem
and at least 1 in summon resistance
the rest in skill of your choosing, or requirements. usually spread into CE or Bone spear and spirit.
as for points you should put all points into energy, and vitality. and enough into strength to wear good armor.
as for a merc, in Hell A2 defensive mercs have thorn auras, making your minions even more dangerous. for difficulties after that use an iron wolf, or maybe a barbarian, or other aura merc.
most of it's up to preference but these are some good guidelines.
i can also recommend some runewords for higher levels