Hi,
We actually recommend keeping them in seperate enclosures their whole lives. This is especially important if they are different species as what suits one probably will not suit the other one.
But the initial quarantine thing (which is what I assume you are talking about ) should last for at least 6 weeks and longer if possible.
In the best case scenario that means in another room at least and with no equipment or anything shared between them - have a search on the boards for some more detailed quarantine info.
As to what species to keep - that's a tricky question. Have you seen any others that you really love the look of?
dr del