Oooooh that cage... Yeah if you buy some wooden shelves to go in there and things like hanging toys, tubes, hidey holes etc it'd be fine. Plus if you buy wooden shelves, you can change where they are in the cage every week so the degus don't get bored

I'm not sure how big the gerbilarium is, it might be too small. You would still definitely need to get another one (Preloved is a good place to start) and introducing them shouldn't be a problem if they are young (Find a way to split cage down the middle and put one in on each side for about a week so they can sniff eachother etc then take the separator away). I think the cage in the pic is an ok size though The bottom wires you can just cover really thickly with hay so their feet don't come into contact with the wire, but it'll still be messy! To reduce mess, you could find a box big enough to put the cage in so that the box reaches up 3-4 inches from the bottom of the cage (if that makes sense) so that hay etc won't fall out

Peace
Akai-Chan