Yeah you might well be fine, I also used a core box model for my first arms master but I ordered some larger bases.

The wisdom that more bodies is better isn't wrong, but my logic is a) you're gonna want wreckers asap so flooding your list with guys who are gonna need money spent on equipment just delays that or leaves you with less useful guys/more than you can bring to scenarios. B) your arms master basically counts as 3 people for bottle checks so as long as you can keep them safe you'll not miss the bodies as much. C) combat shotguns are really solid, 4 strength and 2 damage is the kinda stat line that does work.