I love that dress OP - in fact I bought it but very reluctantly had to return…
I’m a 14/16 with a huge tummy, and they didn’t have a size 4. The size 3 fit me, but (I felt) it accentuated my tummy because it was so snug across my chest (G cup) so I sent it back. Your figure sounds better suited and you can wear it with a bra no issue, the back isn’t that low.
In general I am not a fan of the puffy sleeve vibe that is so prevalent right now, but the fabric on this is so light that it flows really well and doesn’t add absurd volume.
I also spotted someone locally wearing it recently (thinner and taller than me) and it looked great - pulled together but relaxed and not over dressed.
You can definitely wear it with those shoes.
Enjoy your garden party!!