Thanks for the photo, great to see the result! You're right, it's a large tool, I find it easier to hold by one handle, and just push the other end against chest, so that one hand is free to support the wire.
The insulation is usually separated by a thin metal barrier (i.e. when using the tool, without the wire, click it once or twice to just get the crimp held, and then insert the wire, because a metal barrier (with a narrow slot) will have dropped into position after the first click.
Then, the insulation can't get into the conductor-crimping portion of the tool, because the slot only allows the stripped portion to pass through.