I Need Your Help

It’s one thing to write about what to wear to a wedding. It’s an entirely different thing to actually get invited to a wedding and have to figure out what to wear.
I would be freaking out if not for one saving grace – the wedding is in September. I have time to get myself together. But if you’ve been reading this blog for long, you probably can guess that I’m not the greatest at doing that. So…
Okay, my people. Help me please.
I have the Black Annapolis Tomboy Shirt. This shirt is fire, yo. It fits perfectly, it’s a classic look, goes with anything. I love the way the tiny white dots elevate it from a plain black to the eye-catching shirt that it is.
Also in my wardrobe are the Black Leather Suspenders and Ebony Skinny Necktie, which I have worn with the Annapolis Tomboy. I get lots of compliments when I sport my HauteButch duds.
Question: I need to get a vest and/or a suit jacket. What do you think? Opinions needed.
Deciding about the vest/jacket question is not my main problem, though. Here's the thing. My friends are having the wedding ceremony on a Friday night in September in a cool event space downtown. The reception will be right after.
Then Saturday is a party at their house – with a taco truck (O happy day!) and entertainment for kids. So more laid back. Neighbors, friends, family… This is where I’m stumped.
I have no clue what I should wear. Imagine my embarrassment at admitting this. Help a friend out. Please. Look through the HB collection and let me know what you think I should wear to the Saturday party.
Thank you in advance. I have faith that you will not let me down.