Ditto-You don't want to be in trouble with an accidental litter! At least one should be fixed.
In the mean time, get both of them a stuffed animal (appropriately sized, good material that doesn't pull out easy) and put in each of their cages, after a week (so they have the scent) switch them. Now they have a pretend friend, who never bites them and smells EXACTLY like that new rabbit- I think this should help bonding when the time comes.
When you do an introduction make sure it's neutral territory-somewhere Lola's *never* been. Bathtub is usually great-line with towels.
Signs of aggression are obviously growling, but also pinning the ears back, charging, going for the bum. Humping can be allowed as long as it's short lived, tolderated by the other, and not on the face (nipping-..). But that's a while, wait until at least one is spayed!
Ohhh and congrats on your new bunny!! When do we get pictures!!?!?!