Unfortunately levels can cause fights in pairs, so its safest to keep the cage all on one level for groups or pairs.
You'll also want two wheels, two houses and two of most other things as well. Oh and to scatter feed instead of using a bowl.
Groups and pairs can be a nightmare to keep together, but those are all things that will increase the chances of your pair living together happily
I'd also keep a spare cage or large bin incase they ever need separation though. Hopefully it'll never be needed, but the last thing you want is to have to rush around finding something to house a hamster in when they need separation at 10pm on a Sunday or something.