small thing that i have no idea how to do

Everything in that procedure looks like it should work. That's only for a qty 3 though, not 125. You would have to change the number to 125 for it to work.

To make the tamed necromancer summon another tamed AI you would have to make a procedure similar to the one you have above.

For the current procedure, add to it, "set NBT string value to entity" use the [get nearest entity] block and then create NBT name [mod_id:necromancerOwner] set the string value to [get display name of event/target entity]

Then when you have the Necromancer summon the new ai, do "tame [nearest entity] set owner get NBT sting [mod_id:necromancerOwner]"

Oh, I feel a little stupid, lol. For the 125, the issue is there are only 64 items per stack, and it's only checking one stack. You may have to use another local number To be able to get the 125. Later I'll send you an example.

Here is the procedure. I tested it out and it works - https://imgur.com/d30kdYv

For the second half of spawning the Necromancer's "minion" you would need something similar to this procedure. You would need to determine the triggers though - https://imgur.com/wrgyspq 

It depends on what you are looking to do with it.

I'm not really sure I understand your question.

If you're asking about how to determine whether it summons a zombie or a necromancer, I would recommend having separate triggers & procedures for them.

I may also not be understanding your intention with the mobs. I thought you had wanted to have one mob that was tamed summon another tamed mob. For that you would need a procedure on the main mob that does something like "on update tick" if get random chance, do summon tamed entity.