I don't think I would ever try to spawn bettas in a one gallon container....no room at all for the female to get away from the male...or....vice versa....
I would say a 5 is the smallest that I would use, but that's just me....and plenty of plant's and a cave of some type.
On the plaket being mistaken for female thing....yeah, I've had that happen to me the first time I purchased a "female" betta.....lol.....turned out to be a male placket. Beautiful royal blue fella ! I wondered why he got that "gleam" in his eye when I put him in a tank with 2 "other" females.....
Look at the ventral fins....if they are very long than it could be a male. Females usually have shorter ventral fins...but not always. I have one female gold betta with longer ventral fins. I know it's female because of the ovipositor and the girlish figure...lol. Females have a different body shape than the males. Once you know the difference it's easy to tell just by that....usually....there's always the exception.
The white spot shouldn't actually be on the "FIN"...but rather on the body just behind the ventral fins. I'm sure that's what you meant when you spoke about a white spot.
Usually the male is the aggressor, but if the female rejects him....you'll KNOW it ! She'll rip into him like no tomorrow and the poor fella will be left nursing a much less impressive set of finnage.
If you want to breed your bettas, I would set up at least a 10 gallon as a spawning/fry tank.....that way all you have to do is remove the female after spawning...and then the male after the eggs hatch.....and you won't have to remove the fry to something else. they'll be able to grow out in the 10 for awhile. Make sure you have a seeded sponge filter in the tank, and bare bottom tanks are best for fry. Easier to keep clean and also the fry can more easily see any food you put in there for them.
If you use a 10gallon as a spawning tank, you can use the glass from a hurricane lamp to seperate the male and female until they're ready to spawn.
Good luck, have fun....and think ahead to what you're going to do with all those fry when they need to be seperated....
