Although many pet shops encourage selling dwarf hamsters in pairs the reality is that they very often fall out.
It is probably best to keep them as singles. Ron will be fine on his own.
I have a couple of roborovskis (in seoarate cages) and in my opinion, from what I have obseved from the 6 robos that I have owned they love to run and to dig.
Mallow lives in an 80 x 50ish cage with 5 inch deep fitch (soft paper) bedding, a sand tray and a wooden wheel from zooplus.
He seems very cotented.
Maple lives in a 100 x 54cm cage with narrow bars. She has always been very very active and seems to need the extra space.
I think the best way to give space is to give him a cage all on one level.
My robos love meal worms!!! They also like a few soaked porridge oats, raw broccli, nuts (not too many) and teeny bits of cheese.