low on the ground normally means an old queen
Not always the case. Mine congregate on the rose bushes in one of the adjoining gardens.
I have done that. 6 frame nuc with a couple frames removed (careful when replacing them as the bees can be squashed). In fact the only one I went out for this year was scraped from a tree branch whle standing on my car roof (first attempt) using a drawn frame as the 'shovel'. Got her (at third attempt) from a shrubby hedge where she decamped to, from the apple tree.
The other swarm needed a 14 x 12 box and a shallow on top to accommodate it easily. Checked it today and it needs another super, at least, already. Three weeks on, so going well. The parent colony is on a 14 x 12 with three shallows and needs another.
So go prepared, size-wise.