One cannot create skeletons from freshly killed hobgoblins. Those would become zombies.
Skeletons can only be created by piles if bones.
I will discuss this with my DM. I think that medium armor is reasonable, but I am also ok with the skeletons out of the MM.
I do not want to overshadow the other PCs either. Healing is a good schtick because my PC can heal ~185 hit points per day if Cure Wounds is the only spell I cast. If the Cleric did that, she would only cure ~105 points (the Cleric could do more with Prayer of Healing, but not in combat). And the 4 other spell casters who can heal almost never do so.
We already have another multiclass Wizard, so I don't want to step on his schtick too much.
We already have a Druid that conjures animals, so I don't want to step on his schtick too much either.
And since we are losing two heavily armored PCs, that schtick is becoming available again (the best AC in the party is now 18, so my PC will have a 20, front line material).
For the most part, I am quite content to make more modest contributions with skeletal arrows and cantrips (significantly more DPR than a non-necomancer though) and familliar/undead helps, and use a third to a half of the spells for healing, and have the undead use healing potions in combat for downed foes (currently, that is the exception instead of the rule). This frees up Healing Word (and even Mass Healing Word) spells of the other PCs for when PCs drop unconscious.
You can create skeletons out of relatively freshly killed hobgoblins. It's pretty disgusting and time consuming. You are a necromancer. I could see you carefully carving the flesh off a few creatures and polishing some bones, while your companions try to hold down their dinner.