Earlier on in this thread, i read a request for a summon necromancer build guide and unless my eyes are deceiving me, i beleive this thread is lacking one. Here is a good necromancer build that should see you through most of the game solo:
Stat Points:
strength: 100
dexterity: 30
vitality: remaining ponts
energy: 150
Summon spells:
[20] raise scel, [20] scel mage, [20] scel mastery, [1] revive, [1] clay golem, [1] blood golem, [1] iron golem, [5] fire golem (excelent tank with fire aura), [1] golem mastery, [rest of points] summon resist.
Curses:
[1] amplify damage (good for melee scels), [1] weaken, [1] terror, [1] decripify, [1] iron maiden, [1] life tap, [1] lower resist (good for scel mages).
Try to get Trang-Oul set, Arm of king Leoric weapon and a good + to skill amu, rings, charms etc.. This should make your summons stronger, make your curses better and last longer and give you access to some fire skills like "fire ball" and "meteor" (Trang set).
Some people invest some points into "Bone armor" for extra protection but a good summon necromancer should never have to take a hit.
For mercenary, an act 2 heal aura merc with eth insight works really well as a tank and healing support.