Originally Posted by Tihsho
is there any key reason
No, there is no one central consideration. Here's a key reason to house them separately, though: interspecific cohabitation never benefits the animals relative to housing them alone.
experience housing species alone before even considering housing them together. I really can't overstate this. Learning about any species is 95% experience. A fifty word post from some random dude on the internet doesn't even begin to educate you about an animal. Nor does any number of YouTube videos (these are people who eat Tide Pods, remember).
If you think you might like MGs, get a few -- they don't need a large or complex viv.