RobShow gave some good advice: hopefully I can add to it. It is a fun build to play; I wish it wasn't so expensive though.
Not to discourage you from the path of a wizard, but wizards are very reliant on DCs. If you're a first life build you'll probably be running R1s-R2s because your DCs won't be high enough for reliable CC. A few TRs will get you a 36 point build and arcane initiate, which helps. Filling out the thaum reaper tree and getting your sentient xp is a slow grind but essential. With my current summons build I can solo most R6s without perching or kiting for boss fights. R7 is pushing it but is doable depending on the quest. With that said, there are some builds posted here that can solo R8s without any hirelings.
CC is key to keeping your hirelings alive. One thing I don't see mentioned often is dealing with mind-immune enemies (mark of law champs, etc.). I would recommend a specialization in illusion or enchant, then a secondary focus in evo or conjuration. Greater shout and web are important in dealing with those champs. Occasionally teal or the scarecrow will knock down one of these champs, but it's not consistent. More instakills are nice but not as important as CC.
Gold seal hirelings are the key. No matter how much you buff the skele knight, even for a summons-focused build he's the first to die. The best hirelings for a wiz summon build are construct-based, as we have all those repair spells. In tougher boss fights I normally only take the scarecrow and shield golem as I can't keep the rest of the fleshies up. In even tougher boss fights i'll only take the scarecrow as I can't keep the shield golem up. I'll normally have the scarecrow, shield golem, teal, feywild muse, and Albereth (fvs hireling) for regular mobs. If I don't need the healz as much I'll swap out feywild muse for darling for more dps.
Primal avatar is important for the reasons RobShow mentioned. Additionally, I would recommend reborn in fire and spring to summer to help spot heal the fleshies. Normally I take heart nature, then now grow: sky so I can get a mantle of sky. Fatesinger hear my voice friend is also good for some healz during boss fights.
In the interest of pointing out hireling bonuses, harper also has harper leadership if you're trying to eek out more summons power. For legendary feat I would not recommend scion of elysium; you need the DCs more.
In addition to primal avatar, if you're going for a feydark-based build master illusionist is great for bosses: it helps give your hirelings some breathing room to heal. Since you want to go gnome I'd suggest a feydark: 41, pm: 13, then whatever else you want. The pm: 13 lets you get +3 int and +2 enchant and some so-so undead healing with neg energy burst, death aura, and lesser death aura. For epic destinies you'd probably want shadowdancer: 35, primal avatar: 18, and magus for the rest. Alternatively you could go fatesinger: 35, primal avatar: 22 (evasion), and magus for the rest.
Threat management is also important. You want the mobs attacking your hirelings not you. Try to get -90% to -95% spell threat reduction if you can. Even with that there are occasions where I have to use the scarecrow intim button.
Enlarge is very useful for a squishy wiz. Try to get it free, either from feydark, fatesinger, or primal avatar.
For boss fights I also recommend using the legendary wolf whistle before the fight, then swap back to your normal gear. The werewolf is a really nice boost.
For buffs I normally scroll: mass prot from elements, mass bull's strength, mass bear's endurance. Then rage + haste. I will cast resist energy on each hireling if there's a specific type of damage for that boss. You could also scroll adamantine weapons to help with certain boss DR.
Here are the button mappings I use for hirelings:
z: teleport scarecrow (get him away from the veng reaper circles or boss attacks)
x: teleport shield golem (same thing)
caps lock: interact all. focus on an enemy then tell all hirelings to attack it. also good for keeping hirelings focused on the boss.
tab: focus scarecrow so I can heal with reconstruct.
q: focus next enemy (so I can go back to nuking the boss after healing the scarecrow)
windows key: scarecrow intim to get bosses off me
r: reborn in fire (hireling healz)
f: spring to summer (hireling healz)
v: master illusionist (-95% dodge is handy even if it's every 5 min)
3: reconstruct
4: mass repair crit
5: mass repair serious
6: mass repair light