One thing you may notice while looking through this guide, is that it looks incomplete. That's not the case at all, however. I intended this to be a beginner build. A guide to get you started in the league and start punching into monoliths to farm gear with. That's not to say that you CAN'T take this into 500+ corruption empowered monoliths, just that that wasn't my goat with this build. Now that i've set the proper expectation:
Skills
The best thing about this build is that it starts right away. Pick up your minion skills as they become available, and start looking for the routes to increase the numbers of minions.
Pick up Summon Skeleton at level 2. Shoot for the nodes that give you more skeletons: Marrow Walkers, Hollow Walkers, and Grave Walkers give you a total of 6 skeletons rather quickly. From here, you can pick up some minion sustain via Marrow Tap, and then more damaging skills. I decided to make all of the minions archers via Mightier than the Sword, but that's not a requirement by any means.
At level 9, you can pick up Summon Bone Golem. To me Tower of Bones was my immediate route for threat generation. From there, you can get some self-healing through Hunger, and then double the big boys up with Twinned Golems.
Your 3rd skill opens up at level 20, and you have a choice between Summon Wraith and Summon Volatile Zombie. I started with wraith, and then changed to zombies when my last skill opened up at 50.
If you chose the Wraith first, your immediate priorities are to increase his lifespan via Grave Reality and Delay the End. From here, you can shoot for skills to make them hit harder. I picked Reapers, Necrotic Hunger, and Dark Scythe for extra damage, then head to Locus Of Resurrection as a bit of utility.
If you choose the zombies, shoot for Repulsive Vomit and Wretched Innards first off for a big damage increase. Then shoot for Pull of the Grave for the 16% execute. Then go to Ravenous to turn the zombie damage to physical/necrotic.
At level 35, you can pick up Summon Skeletal Mage. At this point, I found the Leech Life helpful early, and then Undead Mortars and Battle Hardened for big damage. From here, you can pick up an extra mage at Order of Death, then go for flat damage.
At level 50, you can pick the skill you didn't choose earlier. Or you can go for better movement through Transplant, bonus damage through Bone Curse, a really big boy through Assemble Abomination, there's a ton of options, and none of them are wrong.
Gear
Gearing while leveling is pretty simple. You want to prioritize PrefixMinion Damage and PrefixMinion Health above all else, pretty much always. When you start getting mid 30s and above, you'll need to start looking into survivability for yourself. Non class-specific idols are a great way to shore up some low resistances, and SuffixHealth plus any minion affix starts becoming more and more common naturally. Start shattering gear as the money comes to you. You can make this character as simple or complex as you like.