If we are setting aside 5e mechanics for a second. . .
I wouldn't even put an arbitrary cap on how many minions a necromancer could have. Give the summon a spell slot, give the summon a decay rate, and let the player figure it out from there. I would also have any undead summons initially come stock with no equipment but the option to arm them with whatever you have found on the battlefield. However, since undead are essentially mindless, I would also give them an extremely rudimentary AI and absolutely no player control beyond equipment and augmentation and also they are always flat footed and have no natural AC beyond any armor or buffs given to them because they are not concerned with the damage they take. Nor can they be healed in any way. Damage taken is absolute.
No additional summons beyond first level, but the ability to use higher level spell slots for summoning to increase, say, the endurance and competency of those same undead which will eventually result in only having a couple of truly badass minions and quite a few trash mobs of varying quality. There would definitely be higher level spells to enhance and buff those summons, however, in addition to the usually array of necromancer shit one would expect to have at their disposal.
So, as an example, first level summon is skeleton, it tears itself out of the exploitable corpse of a downed opponent. It lasts for 12 hours before the magic used to hold it together is no longer sufficient to keep it whole, at which point it begins losing pieces of itself over the next 12 hours until becoming inert. Use a fifth level spell slot and you get that specific corpse in its entirely as a zombie, which moves faster and with greater precision as well as possessing additional strength and hit points. After 24 hours its skin sloughs off leaving a skeleton. At ninth level, the wounds from battle on that raised NPC are healed completely and you get them as they were before they died, all abilities intact, double the HP. After 24 hours they become a zombie, 24 hours after that a skeleton,
You can raise as many undead as you have spell slots, which could be potentially quite a few.
Last edited by DistantStranger; 06/12/20 08:10 PM.