I would want slightly more. I love an expansive meta, not only that, but expansive tournaments would have very repetitive play styles with fewer characters. Then you would need a smaller learning curve to rope in casual players, you'd also need extremely diverse characters while balancing the accessibility because there is already less variety.
Any way that's my opinion on the size,
now on to the actual roster:
A note on your character roster:
Just in general, with the general roster you brought up kinda turned me off. The only difference between 2 and 4 on the outset is the gender. Same with 1 and 5, when I hear 'dark swordsman' I think 'recolored copy with a new super or combo move'. If you had twice the roster I'd be fine because I could experiment with different kinds of characters and discover the nuances of each similar character and how they interact with the other diverse characters, but smaller the roster, the more outwardly diverse you have to be with characters. The average player would think "Why would we need another swordsmen? They're probably gonna play similarly." Which brings up a good point, there's hundreds of interesting weapons that could alter the meta, even something as simple as a spear or brass knuckles and there are variants that are amazingly diverse weapons that are still spears like a Ji and a Fauchard. With 2 and 4, why are they both teenagers with special powers? Unless it has something to do with the story, I honestly think the more diverse they are in the most simple aspects the better, especially if the count of the roster is only a finger more than a singular hand. Make one your teenager with special powers and experiment with the other one. In all fighting games, each character has a concept that makes them different from other characters. Number 3 isn't bad, though I would be wary of the character if his powers weren't highly specific and didn't tell us anything about him. Honestly I think your best concepts are still 1 and 6, because 1, while being done before, could have an interesting backstory and design, while also being a good intro character with a weapon and concept most people who play video games are familiar with. 6, is just plain cool. Anyway, I don't think your character roster is bad, as much as it seems like it's only about 1/3-1/2 of an actual big roster. I don't feel like your current roster could hold it's own just because you have similar concepts for most of your characters while in addition to the size.
Anyway, if you have any questions about building a Roster for a 2D fighter, I'd be willing to help. My friend was making one of these a year ago, and before the project was dropped I helped with editing character designs and concepts. Just PM me if need be, and good luck!