Sudden change in plans

All those things are completely up to you! I would definitely do an arch and a bouquet. To decorate the arch, you could get some flowers from Michaels/Hobby Lobby, etc. and use some wire/floral foam to arrange and attach. I made my bouquet with Sola Wood Flowers, they ship quickly but may not be enough time because it's not the easiest. As for a first dance, again, up to you! I'd recommend keeping it in the middle, don't go too all out, that way your other big day can feel special too, but don't do the bare minimum if you don't want to!

I can't speak to too many DIY projects, as I'm not that crafty. My BMs and I did make our own bouquets with faux flowers, and they came out pretty nice, you can just order silk flowers online to decorate the arch but that seems like a lot of work in a not a lot of time.

You can go as fancy as you want, as it is your wedding! We will be dressing up, I'll wear my dress and BMs will wear theirs, guys will wear matching suits with ties and pocket squares. I would do a first dance still, you don't need to choreograph something if you don't want to. You can go as big or small as you want!

Ooooh I love the look and intimacy of backyard weddings!! The great thing is, you don't have restrictions on decorating due to a venues rules! Something super cute is to have shepherd hooks with mason jars full of flowers hanging as an aisle marker!

Love the arch idea too! Also putting ribbon on the chairs could be fun!