Thinking about something similar, played a character like this back in the days of 2nd edition AD&D...
For BG3, if you're set on the longsword your plan looks reasonable. If you switch to bard immediately, take sword or valor, because they get extra attack at class level 5 or 6. Or go 5 levels fighter and then switch, so you get a fighter subclass and some class features like extra attack and action surge etc.
If you're not set on the longsword you'd have way more options. Scimitar for example with the sword bard. Could also get some levels of Paladin for some smites etc. Really a lot of possibilities to build a gish. But for the sword dancer some form of Bard seems a must
Cheers.
