If it's pronounced Vallen-Teen like most Americans would say it, it's fine.
It'd have a pseud-y feel, imo, as the name of an American who talks like an American. I'd suspect it was a self-name.
But you need not mind that necessarily, esp since you say you are looking for a name with swag.
Valentin formally or on paper,
Val to friends, seems like it would do the trick.
It's timed right. I bet nobody would think it seemed mundane or ugly.
Or even difficult.
Valentin "Vallen-teen" is actually easier for me to say than
Amelie.
However, if someone is apparently an American and talks like one, and lives where fluent French speakers are infrequent and come from elsewhere - but introduces himself to other Americans as Valentin-pronounced-in-French (or attempting the French prn), and insists on that pronunciation ... I would feel like, 'Please just stop.' I might start just calling him
Lestat instead. I can approximate French
Amelie okay-enough, but
Valentin would be next level, I'd need lessons.
- mirfak