Yes there is danger if you get opposite sex of them having babies before six months.
Females can be ready to breed as early as 5 months and you can read about that here
http://www.threelittleladiesrabbitry.com/breeding.php
Here is info on a second rabbit yes or no
http://www.rabbit.org/faq/sections/multiple.html
and a faq on introducing them
http://www.rabbit.org/faq/sections/introductions.html
Hope this helps you!
Pet Health Care, Rescue,Train,Breed
30+yrs pet vet care & nursing, rescue, behavior & training, responsible breeding, small animal care