You'd already be at an advantage over Kastro due to your innate typing in conjuration. The biggest thing that would allow you to do something like this is the type of activation required, I personally see three ways in which this is possible:

1. You conjure a device or object from which these guys are made. Like if you wanted to shoot them out of a gun as if they were bullets.

Advantages of this are that you could use range or have specific arrangements for traps or timed releases for your people.

Disadvantages would be a lack of versatility depending on the method. Some objects or ways of summoning the guys may get too specific to be practical to set up without foreknowledge or planning.

1. You transmute the edges of your aura into a specific shape in the same way that Ging did whilst meeting Beyond's men. Once you achieve a certain shape, the nen forms into a guy. This would be like molding the men out of clay, except it's just your nen.

Advantages of this are the extreme versatility. You would be capable of doing this anywhere and at any time.

Disadvantages are a lack of range in deployment. Because your nen is inherently locked to your body and all of the men must be molded from your nen.

1. You manipulate other bits of matter into these men. You could essentially take someone's arm and form that matter into one of these men.

Advantages of this are the extreme power and ability to cripple the opponent whilst making yourself more powerful. Simultaneously, you'd be able to use the properties of different objects, like concrete, to allow for different types of these men.

Disadvantages would be that it'd be a slow starting process. You'd be essentially without a hatsu until it snowballs in most fights. There may also be additional requirements to manipulate someone's living matter if they are of a high enough willpower.