Having the ability to crop select multiple units would make amassing a large army less headache inducing.
Hey, thanks for the feedback! I agree that moving a large army can be a bit of a headache, and I'm still experimenting with the best UX for it.
I think you may have missed a few features that are already implemented. You can box select units in Attack Mode by dragging while holding Shift and you can create Unit Groups in the Unit Groups window if you want to split your army into quick selections. If you want to gather your entire army, you can also right-click > Gather units here, which will order all of your units to move to that location.
That said, I do agree there's still room for improvement and I'm looking into making large army management feel smoother.