Not good for the fish. One of the other members will explain it better but you need to increase your kh. That can be done using crushed shell from your lps/lfs
Try getting one off a breeder. You don't really want to be breeding a VT female, unless you know for sure the ones you are buying are not VT.
30l is good by like Sam says, it can be done in a 60x30. Personal preference and whatever works for you
I watched my neighbours old keyhole pair spawn about 5 times in the short period he owned them. Never had fertile eggs and they had been breeding for ages :-?
My alpha male L104 lost his first batch of eggs but manged to raise 8 fry with his second spawn. Experience usually makes batch sizes improve. I saw it with my male fighters too.