It's definitely a realistic possibility.
It could end up badly, or it could be okay and nothing will happen. When first introducing them (assuming the male is an adult/ready to breed), the males first instinct will probably be to breed, if the female is not ovulating, she may not like it and give him a little nip, usually the male will back off after that point, but if he persists, the female may become stressed, and serious injuries could come into play, along with the female going off feed due to constantly being pestered by the male.
OR, the male will try to breed, the female rejects him, and they go along their happy lives.
Yes, if you're going to put them together, watch their behavior/if they're eating/ signs of bite marks etc.
Yes, morphs just affect their physical appearance, they stay the same species.
However there are pairings which aren't recommended. Like, enigma x enigma (my opinion, some have done it with success, controversial topic..), and crossing different albino strains like tremper x bell, bell x rainwater, tremper x rainwater.
Yeah, both pairings are fine.