I will tell you both what I have read or been told and what I have experienced.
Most sites will tell you that absolutely under no circumstances can a male and female Betta
live harmoniously in a tank together. One or the other will
kill the other. That is the biggest thing breeders yell about (literally. o.O)
Then I met a breeder who sometimes pairs Bettas off for life, and they never harm one another. She also leaves mother in the tank after they have bred and the fry have hatched (another general big no-no. You take mum out after spawning.) She said she carefully studies the fish, because each is unique and there is no set rule.
Now me, I decided that it was worth experimenting with. Worse case scenario, one or the other gets a bit torn up, I then seperate, medicate, and pamper the heck outta 'em. I realize I was taking a risk, but breeders take a risk everytime they put the pair together to breed. Oftentimes the female gets hurt, sometimes the female hurts back, and other times still one dies.
As luck would have it, my FIRST male Betta (Rama) ever lived happily with two females in his life.
Rama lived with two of his sisters peacefully for several long months, with no problems. Problems arose when Tenkiri and Noelani began to quarrel. I got the impression that one or both wanted to spawn and the other was in the way. Since Tenkiri kept chasing Noelani off, I put Noelani in her own little tank. Rama and Tenkiri then lived happily for many months, before Tenkiri got sick and I seperated the two. Tenkiri never got well, and died. Rama looked quite miserable, so I decided to get another female for him. Jia came next, but she refused to eat from the start, and died after 5-6 weeks of no food.
Rama and Noelani would no longer get along (Noelani tore his fins up
,) so I tried one more new female. I bought Kanya, who was a miniature version of Tenkiri.
Rama and Kanya liked eachother sooo much that when I had Kanya in a bowl, preparing to put her into Rama's tank, she JUMPED out of her bowl and landed in his tank...! Tricky little lady she was. They lived together a long time with no problems. Regrettably, Kanya then got sick and no medication I had or bought would help her. They were seperated, and she eventually died. Sigh. Rama was alone again...
I got two more females later, who I still have, and gave them each a chance with Rama. Suchin and Mali both hated Rama.
So I just let Rama live alone, which he adjusted to just fine. He eventually passed away of old age, I believe, since he had NO symptoms.
My feelings are that it's a considerable risk to put males and females together, or even females together. You have to introduce them on neutral territory, so neither feels like their home is being invaded. You have to supervise them a lot at first, until you have a feeling of what they're like with eachother. And you have to be ready for emergencies, problems, or to just admit they don't care for eachother.
I think it can work out, since fish are unique individuals. But it isn't easy to pair up two. You have to get a good feeling of what they're like. Two submissive fish are more likely to get along then a submissive and dominant. They need to be on equal footing, I think.
I also think it would be perfectly fine to give it a try, if you wish. Just be prepared to have seperate homes in case it doesn't work out. Oh, and keep some good, all-around anti-fungal and anti-bacterial meds to prevent infections if tails are torn up.
What I would probably do with that 30 gal tank you've got is buy or make some dividers and keep the male alone in 5-10 gals and put several females in the 20-25 gals left. If it's a good divider, they can see eachother and interact through it, but obviously not harm eachother.
Just introduce the females to their side all at once, so no one is singled out as the new girl, and there's less likely to be problems.
In closing, you have seen what a female can do to a male, and I'm sure you can imagine what a male can do to a female. Lifetime pairings/co-habitation is possible between males and females, though risky. It is, however, no more risky than trying to breed them and I wish some breeders would realize this rather than yelling at and insulting those who decide it's worth the risk. It is totally up to you whether you give it a try or not. Only you will know your fish and know what they need/want.
JSYK, the reason I even decided to risk putting males and females together is that I feel my company is often inadequate. They need other fish, and since I could get no clear answer on what other species I could mix with Bettas, I decided to give male-female co-habitation a try. I want my fish to at least
see eachother, if not be able to live together. I feel their lives are less interesting and less satisfying without roomies.